If you are interested in efficiency have a look at this;
Twin-R
Only of academic interest in the short term. Dyn Aero went bust a few months ago with the twin ¾ of the way through its certification. The company has been bought as a going concern and spares etc are back up and running but no word yet on the plans for the twin. The efficiency comparison charts make interesting reading though.
Tecnam are reported to be working on a Rotax 914 turbo version which should make a big difference to the aircraft.
Rod1