Unless there is a demand for something completely different (Tailwheel/Aerobatic/IFR-deiced) I would go for another Robin.
Can be used by all as they all fly the same and a known quantity (if not the factory!)
If you want to go for something different get a Cub/Cap or a Diamond Star if feeling flush.
Robin now do a diesel version as well which obviously would bring operating costs down quite a bit.
Have fun choosing and flying it!
FD