Out of all the Zelda games I have played I like the original sword in The Legend of Zelda for the NES because it could send out a beam when at full health.
Biggoron's sword ALLLLL THE WAY! Aha, I specifically got it so I could beat Bongo Bong in 30 seconds. It was then the easiest battle of my life<3
Though...I didn't realize that I had to use the Master Sword to defeat Ganon at the end, so that took me FOREVER, wondering why he wouldn't die....lol XD
The only game I have not finished right now is Majora's Mask. So off the top of my head I would say that the four sword was my favorite sword because it had the ability to split Link into multiple parts. If the tiles that made Link split were analyzed in more depth they could be put to some interesting uses.
So hard to say... My favorite would have to be the Gilded Sword. Its amazingly cool looking, and extremely powerful. Second place for me would be the Great Fairy's Sword, extremely powerful and an item, rather than weapon. followed by third place Biggoron's Sword from Ocarina of Time.