Stick with the Avistar for a while to practice your landings with your instructor. The landing gear on those are really forgiving and you won't feel too bad if you goof a landing, damaging the plane. After you've got that down to a science I'd go for the Mustang PTS. It's a fantastic flying plane with no real bad tendencies. I actually think it flies better than the Avistar, plus it looks cool! The only piece of advice I can think of is to take off the speed brakes on the landing gear. They seem to force you to run the engine harder to keep up your airspeed.
Also, I'd pick up something like a Zagi for a 2nd or 3rd plane. They're pretty simple to fly, mostly right stick, and are very exciting. Plus, they're easy to land. You just turn off the power and keep the wings level. They'll practically land themselves. Good luck!