One would have to ask "what do you want out of a second plane?" If a person is getting bored with a trainer type model and wants to have more aerobatic capabilities than a good semi-symetrical low wing with a constant cord and low wing loading will suffice. It is possible to take a trainer and
"bash" with modifications and make it just as maneuverable as the above mentioned. If a person wants a challenge of building I suggest building off of plans. My first low wing was kitted and built with plans from RCM. I am guessing that the Question of "Good second plane" means to step up into a low wing. Although in my opinion any second plane which interests the individual is a good step toward the experience of RC flight. And as you progress you will realize the lazy flight of the trainer can be just as fun as that "Hot" plane.