In the US you'll find it very hard to find CB American treefrogs. I had CB Gray TF froglets available a few months ago but there was almost zero interest and now I have none. I plan to breed my adults again late next spring so that's a possibility.

Regarding hardiness, definitely the Gray Tree Frog. Greens are a more humid and warm region frog - look at the distribution maps on amphibiaweb. Greens are also kind of skinny and wimpy looking in my opinion. The other option, and these are available from Salty City right now (Leonard had WC adults lay eggs while he was trying to sell the adults) is the Barking Tree Frog - Hyla gratiosa. Think of it as a much chunkier version of a Green. They feed very well, are very pretty (they are almost as versatile in colour range as Gray Tree Frogs) and they are slightly larger than adult Gray TFs.