Kind of like asking about scotch. I think it's a matter of personal taste. Some like bleands, some like single malt, etc.
I like Patron. I know it's pricy, but I don't really drink much, so if I'm going to get some, I'm sipping and enjoying, I get what I like.
As was said earlier, if you're using it to make margaritas, than pretty much any tequila will work, so don't waste your money. Might as well get Jose or even store brand.