I've been to Fenway, Shea (the old one), Camden Yards, Turner Field (now gone), Chase Field, Marlins Park, Guarantee Rate Field (when it was US Cellular Park), Miller Park, Petco, and AT&T Park.

Of those, Chase, Petco, Camden, and AT&T were my favorites, with AT&T being the overall best (even though it was April and about 50 degrees.)