My recommendation is to first find out what the guys are flying at your local flying field. Usually the most popular brand and model at the field is the best engine. Why? These guys have experience with these engines and no how to properly set them up and how to keep them running. My field is an OS field by a large margin. Go to another field and those guys all swear by Saito or some other engine. Who is right or wrong is primarily based on what the guys at your field fly the most. Set-up and experience have just about as much to do with engine performance as the design. I am an OS guy and have had nothing but very positive experiences with them. Super Tiger makes a good glow engine for less money, but they can be hard to adjust. Mokie also makes good engines, but they too can be difficult to adjust and seem to vibrate more on the larger engines. We have a few Saitos at the field and for the most part they seem to run well, but here again, I am partial to OS. Not all models within a brand are of the same quality. Each manufacturer has their dogs. For value, performance, reliability, user friendliness and service OS is among the best IMHO

BTW - for a trainer, a 40 LA is hard to beat based on cost and what a new pilot needs as a beginner. Why anyone would want to rip the engine and the servos out of a trainer anyway is beyond me. Sell the trainer as is and then upgrade the engine and electronics to match the plane. Go on the high end of the power range when selecting an engine and then use throttle management to control speed. Nothing better than having the power to get out of trouble when you need it. Nothing worse than wishing you had more power and none being there. Just my 2-cents.