LOTS to pick from!! If you want to move to low wing, tail dragger you`ll get a lot of folks who`ll recommend Sig 4* series, and they are an RC classic design for sure. Flew one as a second plane and liked it very much. The Tiger from Carl Goldberg is another " standard " for a second plane. You could also look at H9`s Pulse. I`ve started flying one and like it very much. Good sport plane for aerobatics and is great with a good 46 up front. Would be fine for a second. If you want to stay with a trike, might want to consider the World Model T-34. SUPER airplane. Steady as can be, a real sweet flyer, likes a little speed on landing ( at least mine seems to ), and is a nice looking sport scale plane.

By the way, keeping your Avistar? I think it`s a good move. ALWAYS better to have more than one plane, and the Avi is an excellent one IMHO. Soloed on one four years ago, still have it even though I fly other planes, and have always been glad I kept it.