That's hard to say mate. I won't vote for now, but I am gonna go with 09-10 as I feel Barca were still at peak of powers after the treble and really should have beaten Inter in the CL semis. Though Villa hadn't been bought yet by that point, and I consider the 10-11 team the pinnacle of Barca.
In 12, Pep was starting to wind down and I feel the team felt it a bit. I wasn't following La Liga enough in 1993 (Sky or BSkyB as it was then was in its infancy and I don't think La Liga was shown, plus I was only 10). 06-07 I don't remember that well. 15-16 seemed decent but I am gonna go with 09-10.
I should make clear to you I am not a Barca fan (though I do like the club) so I am not as intricately familiar with every season as people here. I still consider Pep's Barca the best team I have ever seen, though.