I've instructed on most every trainer type... Here are my impressions..
Avistar = Awesome, just get the ARF, and buy any .46 BB engine, also glass the wing center... My top recommendation.
Superstar = Gentler than the Avistar, doesn't "grow" with you like an avistar.
Nexstar = Good with the AFS system OFF, tough to control when the AFS is fighting the instructor.. Not an inexpensive alternative. Good though.
Eagle = Big slow, lumbering.
Kadet = Big slow, lumbering. Floats well.
If you're training on a buddy box, a good instructor will 95% of the time save your plane, thus I recommend the Avistar.
If you're learning by yourself... first: good luck, second: I'd go with one of the more gentle planes listed.

These are just my humble opinions.
I love it when a student shows up with an Avistar ARF (not RTF) and a .46 BB in the nose.... Means I get to have some fun too!
Best of luck.
Dave