There have definitely been hardest or easiest game threads before, but I couldn't find one ranking them all so here we go. This is extremely subjective as there are multiple factors that go into difficulty like combat and puzzles so there could be a wide variety of opinions. Here is mine ranked 1 as the hardest and 17 as the easiest.
1. Adventure of Link - This has the most difficult combat in the series by a very wide margin. Puzzles are rare, but the ones that exist are obscure. Navigating dungeons late in the game is also challenging.
2. Oracle of Ages - This has the hardest puzzles in the series, and the combat is middle of the pack for a Zelda game. I think the dungeons in this game are the most complex in the series even including 3d games.
3. Oracle of Seasons - This game has some pretty difficult puzzles as well. I think what is overlooked is the overworld puzzles involving changing seasons. The dungeons in Ages are more difficult, but navigating the overworld and solving puzzles in the overworld in Seasons is more challenging as there are four variations to the overworld.
4. Legend of Zelda - I think this game has the second hardest combat in the series. Wizzrobes and darknuts are both really challenging. Other than level 9, I don't think navigating the dungeons is particularly crazy though, and the puzzles are basically nonexistent.
5. A Link to the Past - Combat is tough but feels much more fair compared to the first two games in the series. Puzzles start to exist on a more regular basis, and the dungeon themes lead to some clever dungeon designs like Skull Woods.
6. Tears of the Kingdom - TotK I think is pretty clearly more difficult than BotW, but they are similar. The weird thing about these games is the reverse difficulty curve in which things start off killing you left and right, but by the end you're unkillable. TotK has similar puzzle difficulty, but I think the combat difficulty is what puts it above BotW with the additions of certain overworld enemies. Dungeons are not particularly difficult but have some clever puzzles as do the shrines.
7. Breath of the Wild - Combat is more difficult than the 3d games that came before it, and puzzles were unique. Shrines were the highlight of the game, but the Divine Beasts all had interesting puzzles as well. Vah Naboris stood out as the most difficult.
8. Spirit Tracks - Puzzles are pretty great in this game with good variety. Combat isn't anything special due to the controls. I think this game deserves bonus points because you can just randomly end up at the game over screen due to mistakes with the train in the overworld. Also the end of the game is really challenging.
9. Link's Awakening - This game is the basis for the Oracle games so it's similar but simpler in many ways. I think this game is the first that really put significant effort into puzzle design, and there are some confusing dungeons as a result.
10. Skyward Sword - I prefer the button controls, but the combat is much more difficult than the 3d games that preceded it because of having to control the angle of sword swings regardless of which control method you use. I wouldn't say any of the puzzles are particularly hard, but they are very clever and thoughtfully designed.
11. Phantom Hourglass - The Temple of the Ocean King is pretty challenging and unique for the series. You could possibly die in the overworld, but not nearly as easily as in Spirit Tracks. Combat isn't difficult, but the puzzles are at least thought-provoking.
12. Majora's Mask - I love the time mechanic, but I hear people complaining about it often so that is a factor in the overall difficulty. The puzzles and dungeons can be challenging at times. One thing that I haven't seen mentioned before is that being child Link makes combat a bit harder than Ocarina of Time despite being essentially the same. Also some minor changes can make combat more difficult. Specifically I'm thinking of the Iron Knuckles in Ikana Graveyard. I find myself having to pay much closer attention fighting these Iron Knuckles than Iron Knuckles in OoT.
13. Minish Cap - I think this game has a reputation for being easy, but I think there are some difficult moments along with a very difficult final boss. Some of the overworld puzzles in between dungeons can be challenging as well. Dungeons aren't particularly easy or hard.
14. Twilight Princess - I think if you ban most of the hidden skills, combat can actually be difficult, but that's a choice to make the game harder so I don't give much credit for that. If you gain the hidden skills as they become available, nothing in the game should be hard to fight except maybe King Bulblin on horseback. Puzzles and dungeons are well designed and have some thought provoking moments. I can see people having trouble with the Master Sword puzzle as well.
15. Ocarina of Time - Combat can be difficult at times, but with patience anything can be defeated without much trouble. If you go around with bottles with fairies, you realistically should never die. Puzzles and dungeon design I think are similar in difficulty to MM and TP. A lot of the puzzles in this game are now cliches, but this game either invented them or was the 3d interpretation of things from ALttP and LA.
16. A Link Between Worlds - I read somewhere someone explained that the puzzles in this game are so intuitive that they are all easy, and I think that's a fair assessment. The design around knowing which dungeon item a dungeon revolves around before you enter it limited the puzzle design. I want to clarify that I love the nonlinear approach of this game, but I think they could have done things a touch differently with respect to the items and made things better. Combat is also pretty easy, but there are a handful of enemies that can cause concern.
17. Wind Waker - I love this game, but I also think it is very easy. Combat is incredibly easy with the parry system. Even the Cave of Ordeals isn't particularly challenging. Puzzles and dungeons are well designed but nothing stands out as particularly difficult. The only part of the game in which I've come close to dying in Dragon Roost Cavern because you only have 3 hearts and one bottle. Once you have more hearts and bottles, it gets easier.
1. Adventure of Link - This has the most difficult combat in the series by a very wide margin. Puzzles are rare, but the ones that exist are obscure. Navigating dungeons late in the game is also challenging.
2. Oracle of Ages - This has the hardest puzzles in the series, and the combat is middle of the pack for a Zelda game. I think the dungeons in this game are the most complex in the series even including 3d games.
3. Oracle of Seasons - This game has some pretty difficult puzzles as well. I think what is overlooked is the overworld puzzles involving changing seasons. The dungeons in Ages are more difficult, but navigating the overworld and solving puzzles in the overworld in Seasons is more challenging as there are four variations to the overworld.
4. Legend of Zelda - I think this game has the second hardest combat in the series. Wizzrobes and darknuts are both really challenging. Other than level 9, I don't think navigating the dungeons is particularly crazy though, and the puzzles are basically nonexistent.
5. A Link to the Past - Combat is tough but feels much more fair compared to the first two games in the series. Puzzles start to exist on a more regular basis, and the dungeon themes lead to some clever dungeon designs like Skull Woods.
6. Tears of the Kingdom - TotK I think is pretty clearly more difficult than BotW, but they are similar. The weird thing about these games is the reverse difficulty curve in which things start off killing you left and right, but by the end you're unkillable. TotK has similar puzzle difficulty, but I think the combat difficulty is what puts it above BotW with the additions of certain overworld enemies. Dungeons are not particularly difficult but have some clever puzzles as do the shrines.
7. Breath of the Wild - Combat is more difficult than the 3d games that came before it, and puzzles were unique. Shrines were the highlight of the game, but the Divine Beasts all had interesting puzzles as well. Vah Naboris stood out as the most difficult.
8. Spirit Tracks - Puzzles are pretty great in this game with good variety. Combat isn't anything special due to the controls. I think this game deserves bonus points because you can just randomly end up at the game over screen due to mistakes with the train in the overworld. Also the end of the game is really challenging.
9. Link's Awakening - This game is the basis for the Oracle games so it's similar but simpler in many ways. I think this game is the first that really put significant effort into puzzle design, and there are some confusing dungeons as a result.
10. Skyward Sword - I prefer the button controls, but the combat is much more difficult than the 3d games that preceded it because of having to control the angle of sword swings regardless of which control method you use. I wouldn't say any of the puzzles are particularly hard, but they are very clever and thoughtfully designed.
11. Phantom Hourglass - The Temple of the Ocean King is pretty challenging and unique for the series. You could possibly die in the overworld, but not nearly as easily as in Spirit Tracks. Combat isn't difficult, but the puzzles are at least thought-provoking.
12. Majora's Mask - I love the time mechanic, but I hear people complaining about it often so that is a factor in the overall difficulty. The puzzles and dungeons can be challenging at times. One thing that I haven't seen mentioned before is that being child Link makes combat a bit harder than Ocarina of Time despite being essentially the same. Also some minor changes can make combat more difficult. Specifically I'm thinking of the Iron Knuckles in Ikana Graveyard. I find myself having to pay much closer attention fighting these Iron Knuckles than Iron Knuckles in OoT.
13. Minish Cap - I think this game has a reputation for being easy, but I think there are some difficult moments along with a very difficult final boss. Some of the overworld puzzles in between dungeons can be challenging as well. Dungeons aren't particularly easy or hard.
14. Twilight Princess - I think if you ban most of the hidden skills, combat can actually be difficult, but that's a choice to make the game harder so I don't give much credit for that. If you gain the hidden skills as they become available, nothing in the game should be hard to fight except maybe King Bulblin on horseback. Puzzles and dungeons are well designed and have some thought provoking moments. I can see people having trouble with the Master Sword puzzle as well.
15. Ocarina of Time - Combat can be difficult at times, but with patience anything can be defeated without much trouble. If you go around with bottles with fairies, you realistically should never die. Puzzles and dungeon design I think are similar in difficulty to MM and TP. A lot of the puzzles in this game are now cliches, but this game either invented them or was the 3d interpretation of things from ALttP and LA.
16. A Link Between Worlds - I read somewhere someone explained that the puzzles in this game are so intuitive that they are all easy, and I think that's a fair assessment. The design around knowing which dungeon item a dungeon revolves around before you enter it limited the puzzle design. I want to clarify that I love the nonlinear approach of this game, but I think they could have done things a touch differently with respect to the items and made things better. Combat is also pretty easy, but there are a handful of enemies that can cause concern.
17. Wind Waker - I love this game, but I also think it is very easy. Combat is incredibly easy with the parry system. Even the Cave of Ordeals isn't particularly challenging. Puzzles and dungeons are well designed but nothing stands out as particularly difficult. The only part of the game in which I've come close to dying in Dragon Roost Cavern because you only have 3 hearts and one bottle. Once you have more hearts and bottles, it gets easier.