This is strictly draught beer availability, now. Lots of bars have an extensive selection of bottled beer but may only offer the “Big Three” on tap plus a token import like Guinness. Personal testimonies are cool but if anyone actually has a line on what bar officially has the most draught beers in the world that would be completely bonus.
I know that I can not answer this one, but if you are in the ATX-check out LoveJoys. They have a lot of great tap selections.
Eleusis - I have been to that Taco Mac and can confirm they have an enormous number of beers there (but will admit that I never counted).
They have even more beers available in cans/bottles. We used to go there, look at the four page beer menu and try to pick the most obscure beers we had never tried before. Amazing place.