Is the Avistar the only plane you've ever flown? If so I'd recommend maybe something like a 4*, a stick, Tiger 2, etc. Although I will say that the UCD will fly like a gentle giant if you set it up correctly. No one can really give you concrete advice without seeing you fly. Generally though, you wouldn't think of a UCD as a step-up from an Avistar. It would make a good third plane. Get some experience on a low wing trainer type plane before looking at a 3D aircraft.