RE: good second plane
If you have mastered the high wing trainer then I think that the next logical move is to master a low wing trainer, there are a lot of options here and I just can't remember all the low wing trainers but I will mention a few of them:
Kyosho, Calmato low wing trainer
Sig Four Star 40 low wing trainer
Tower Hobbies Voyager low wing trainer
Carl Goldber Tiger Low wing trainer
Any of those mentioned planes will last longer on your thumbs than any High wing trainer, because you now will learn some aerobatics maneuvers and they are capable to perform them flawlessly with a bit of forgiveness.