Can't say there is one single show that was the best, but my tops are:
Zion I - I've seen them 6-7 times, but last time they came they did a 2-hour set that blew my mind, and Minnesota played after, which was neat.
Paper Diamond - Had never listened to him prior, and he fucking killed it. Danced my face off.
Ghostland Observatory - So many LAZARSSSS
Gramatik - In a packed small venue. Super groovy.
AFI - In the pouring rain at Warped waaaaaay back when.
The Roots - because The Roots...
Honorable mentions to: Slightly Stoopid, Bassnectar, Damien Marley and People Under the Stairs