I've been to a lot of stadiums- Boston, Minnesota (old), San Diego (old), both Chicago's, Seattle, Tampa, Pittsburgh, DC, Anaheim, LA, Toronto, Oakland, Baltimore, KC, Detroit, St Louis (old), Cincinnati, and Milwaukee
I'd have to say Seattle, Boston, Pittsburgh, Milwaukee and LA were my favorites in no order
For sentimental reasons DC was awesome (PM for details)
I'd love to go to SF and see a series, with 1 game sitting in the upper deck for a view of the ocean. I was planning on Atlanta this summer for the ASG festivities but the idea that fans will be allowed appears less and less likely as days go by