Hi there
your on the right track, always look towards CB frogs, pretty sure the basic care applies to pretty much these three species, for more information go to the care guide on the forum. I personally would choose the surinam or brazilian because they greatly resemble the wild frogs and have huge ''horns'' although captive bred surinam are rare. the cranwells horned frog as described in the care sheet start out as a bright green but as they get older, they may turn into a more brown color, these frogs are also available as albinos. Ornates would be my second choice because their color intensifies as they get older and i think that the "Hi red" would be spectacular.
For exo terra tanks, i personally think that the 12x12x12 is too small but the frog isnt going to move much, the 18x18x12 would be in my opinion a better choice, you would have room for a large waterbowl (make sure its not too deep!) and other acessories, you can always check with other horned frog members on the frog forum