I have a LT40 with a 46 la - plenty of power for the trainer, but I wish I bought a 46 FX for it. I could then use it in many more different airplanes. The LA is more weight for its power and sport planes are more fussy about weight. When I first started I didn't know much (still don't) and was more worried about the Hobby store upselling me.

Either way you won't go far wrong with an OS engine.