Since most trainers these days are quite adequate, my opinion is you can't go wrong with a .40 size ARF. The one splatt recommends is probably just fine. I'd recommend the Sig LT-40, or the Solo Sport, as my students have had great results with both.

Also, I usually recommend a .46 ball bearing engine, but have seen some .46 LA's lately which were more than adequate.

Still can't decide? Ask a local for a good used plane. Good luck!

Dave Olson