1. Smash Switch - Completely unexpected for me in this March Direct and very well done with the Splatoon 1 trailer bait and switch.
2. Brawl - Great cinematic reveal trailer with Solid Snake being such a surprise at the end. Don't think a Smash Bros. will ever catch people off guard again like Brawl did with third party characters.
3. Smash 4 Wii U/3DS - I loved the Villager receiving an invitation to Smash leading into the character reveals.
4. Melee - The opening cutscene to this game is my favorite of the franchise, but considering I already played the game before watching the reveal, it doesn't do it for me.
5. 64 - Never watched the reveal trailer, but I've never been a huge fan of the original Smash Bros. either way.