I actually got around 10 or so emails when that poll went up a while back going into fine detail on why I am the worst person on the planet for not calling it Los Pegasus instead of Las Pegasus. They also stole my cat.
It looks like the folks voting for "Las" were in the right though! Vegas was the intended city according to M.A. Larson on Twitter. Casinos, Magic Shows, Showmares, and more can be found in Equestrias Very own Sin City.
Now give me back my cat!