i'd go for the 55 gal...just because your africans are cichlids right? they get big, and might beat around the adfs
if your adfs are real young though, make sure they have a place to rest close to the top, this is gonna sound stuipd but a real tiny adf of mine had trouble making it up to the top often, and i thought he might drown, before i could do anything i found him in my albino clawed frogs mouth
i know clawed frogs get to be jerks when they get bigger, but he was still kinda small at the time, and i doubt he decided to snack on another frog, i think baby drowned and then clawed frog found him though
just make sure the frogs can rest near the top of the surface, and make sure they can still have places to hide