Choosing a second airplane depends a lot on your flying skills and those of us on RCU can not judge them.

If you are young and have good hand-eye coordination, then a more advanced plane will suit you. On the other hand, if you are older or are not good with hand-eye tasks, you might want to get a plane that is not too much advanced over a trainer.

In most cases, a "Stick" type, shoulder wing plane with a symmetrical airfoil will normally do. Several companies in various countries offer them. You might also consider the Kangke SK/50, another shoulder wing plane, but one that does not have "Stick" in its name.

If you insist on a low wing plane, it is hard to beat one of the Sig 4-Stars, either ARF or kit. With the full wing, they are still quite trainer like. With one rib clipped from each side, they roll faster and will do virtually all advanced aerobatics except serious 3D.