I've seen Yes 5 times, more than any other artist starting with the Fragile tour going up to Union. They're one of my favorite post-Beatle era bands along with ELP, King Crimson and Zappa. After The Beatles split, I just progged-out big time.
As for the best lineup, I'd probably go with the Fragile/CTTE set. As a former drummer myself, Bruford is definitely the one. However, Relayer is one of my favorite albums, almost on par with CTTE. Bringing in Patrick Moraz on keys gave a nice fresh jazzy feel to their music, instead of Rick's constant classical musings. Fusion was getting quite popular in '74 with Mahavishnu, Weather Report and Return To Forever, so Yes took the smart step and followed along. That album was a real breath of fresh air after the over indulgence of Tales (I fell asleep during the show on that tour! Still not a bad album though). Never really liked the Yes West (with Rabin) stuff much. I was in the Navy at that time and when I saw people dancing to Yes in the clubs, I knew something wasn't right!