I haven't been to all of them, but I'd rank the ones I've been to as follows:
1. Giants - best location for pre and post game fun, loads of talent
2. Dbacks/Rox - great crowd, awesome shiny new stadium that's often filled to capacity with ladies suntanning on the lawn. Best stadium and it's not even close.
3. Angels - it's closest to my work
4. Dodgers/White Sox - they built it too big, but it's nice though NO SHADE IF ITS REALLY HOT
5. A's - nice, easy location. all bleacher seating sucks though. ETA: Nevermind the bleacher thing. They upgraded it last year. In fact, I sat in one of the new dark green plastic seats and burned my ### off.
6. Mariners/Padres - it's been a few years since I've been. it was nice enough, but nothing stuck out about the experience