BL2 is the better game of the two. It's a stunning game. I would add get the GOTY edition.
BL1 is harder to get from A-B and back again, (and I actually got fed up in BL1.) Someone will argue with me on that, but it's true. Therefor BL2 is more fluent, and my guess is you will not want to stop playing.
I played BL2 last year and wasn't even sure I'd like it. It was so much fun it took my head clean off. Everything, even the cartoon weapons, are epic. The graphics are truly amazing.