I have two gliders. Which size pop up is the best size? I'm thinking either the medium should be adequate but I'm willing to go with the large if "bigger is better" thanks.

I think that the Medium should be fine, that is what we went with and it is plenty big for our two girls, see this post for details in this thread:

http://www.glidercentral.net/ubbthreads/..._ca#Post1389614

Phil

You are all brilliant! I've been looking for a travel cage that would be easy to store (little to no storage in my apartment) and wouldn't break the bank, and you geniuses found it! The pop-up kennels are a great idea!