I'm 34, so I missed most of my favorites. I'm pretty envious of guys who've seen Led Zeppelin, Hendrix, The Doors, Black Sabbathm etc. My father grew up in Westchester County, NY (just north of NYC) and saw pretty much every band of that era. One of his favorites (other than Woodstock) was seeing Clapton and Santana on stage together.
I've seen a bunch of concerts, and it's hard to give a top 5, 10, or any other number. I think that a lot of them are different, not necessarily better. Their have been a few bad ones though.
The best concert I've seen is pretty easy though -
Metallica in Albany, NY in 1992 touring for the Black Album.
No opening band. Just Metallica playing for about 3 hours straight. This was back when they played with an attitude. I've seen them twice since. They now play like a bunch of guys who are having a great time playing music, which is good in a different way. I prefer Metallica to play pissed off though. It makes songs like Creeping Death and Battery a bit better.
I saw them in MSG last November. Excellent setlist. They played several live rareties like Trapped Under Ice, Dyer's Eve and Shortest Straw in the same night. Very cool.