They are very similar so I would lean towards whichever one's menu better appeals to you. FWIW, my nephew prefers T-Rex (because dinosaurs) while my niece prefers Rainforest. Not sure if other boys and girls are like that too!
I'll also add that you can find Rainforest Cafes in several major cities (we have one here in Niagara Falls), so even if you don't have one at home, you may find one somewhere else in your travels at some point. To my knowledge, the T-Rex at Disney Springs is the one and only location.