My suggestions must be quite general because I do not know what trainer you are flying nor how skilled you are. In my opinion your current skill and future goals should help you decide what to do next. I strongly reccommmed that you continue to practice/improve your flying skills and to gain new skills.

While choosing and building your next plane fly your trainer. Concentrate on improving and perfecting your skills in controlling the flight path, maintaining altitude in turns and constant rate of roll and stability of the bank angle, and the roundness of loops. Most especially work on consistant, smooth take offs and gentle, controlled landings.

I suggest your choice of a second plane be a well behaved "sport" plane, with a 'tricycle' landing gear (nose wheel and main gear). There are many from which to choose, and some of the better ones have already been suggested. Depending on which planes are available to you, you might also consider ( sized according to your budget and your ability to transport it);
a). High Wing type -- an "Ugly Stick" type,
b). Low Wing type -- such as Goldberg 'Tiger 2' or the World Models 'Super Sports'