Oh this is tough...Robin's really hyped me up...I mean Captain Falcon was also revealed there too which was awesome, and in the way of a Fire Emblem boss battle? Yes please. And they put Robin in and he/she works exactly as I hoped they would, male or female, swords AND magic...
Shulk's was the one I watched the most by far, but I think that was due to the music, I loved the cinematic of his jumping Bowser and then fending off Marth and Link and the gameplay got me excited too, and I didn't even know who he was! I actually bought Xenoblade Chronicles shortly after that trailer came out and I'm loving it.
Pac Man too...but that was more just hype rather than the trailer being good, wasn't bad but he didn't have any real cinematic or anything else special until the very end.
Probably my top 3.
But Greninja/Charizard was awesome, the animation we got plus we got gameplay of both of them AND got to see Lucario's FS.
Honorable Mention go to Palutena vid, but just because of that animated fight between Pit and Link (I don't even like Pit but it was cool)