OK, here is my list. I'm including past and present stadiums. I grade them roughly like this:
Atmosphere - 60%
Aesthetic - 25%
Neighborhood/Misc - 15%
I don't care about food options or how easy it is to find a bathroom or whatever. Just going off the level of enjoyment I had at the game and how nice the park was.
1. Wrigley Field
2. Oracle Park
3. Fenway Park
4. Old Yankee Stadium
5. Camden Yards
6. Old Comiskey Park
7. Kauffman Stadium
8. Guaranteed Rate Field
9. Nationals Park
10. Chase Field
11. Miller Park
12. Great American Ballpark
13. Qualcomm Stadium (SD)
14. Angels Stadium
15. Metrodome
16. Olympic Stadium (could have been influenced by my 19 year old self being able to buy tons of cheap beer)
17. County Stadium (MIL)
18. Memorial Stadium (BAL)
There are also about 7-8 ballparks that I've literally walked around the perimeter of and peeked into the park but they weren't in town while I was, but I especially loved walking around Petco Park and Minute Maid Park, not as much Citizen Bank Park and Dodger Stadium (both surrounded by miles of parking lots)