For me, all of the pre '94 shows I went to were at the top of my list. Nirvana, Mudhoney, Soundgarden, Melvins, Pearl Jam, etc. I saw them numerous times that I can remember, and some times that I can't remember, those were good too.

Recently there have been numerous "best" concerts including but not limited to Zappa plays Zappa, Dave Matthews, Iron Maiden, Alice in Chains, Tony Bennett, and Stone Temple PIlots. Out of those, I would say Stone Temple Pilots at Berkeley Greek Theater in 08 was my favorite. I have tickets to both AIC shows next month