Is there a way to tell if a pumpkin is going to be good for cooking?
Many of the varieties of pumpkin sold in US stores in the fall are decorative -- they're grown for their appearance and size, not for cooking with.

Ask for 'sugar pumpkins' or 'pie pumpkins' at your grocery store, farm stand, or farmer's market, and you should be able to find them -- they tend to be smaller, more squat than round (although, some farmers markets might have other varieties of "pie" pumpkins).

If you can't find them -- I'd go with acorn squash, instead of using one of the decorative pumpkins.