Personally I am thankful I learned this season on a two stroke - it allowed me to spend less time tuning or learning how to tune and more time flying.

That being said, if I were going to buy a four stroke for a trainer, would opt for one on the larger side so that I could take it out of the trainer and put it in my next plane where I would be more likely to appreciate the low end power and scale-like sound of a four stroke, and then buy a cheap two stroke to throw in the trainer for the few days I'd actually fly it once I moved past flying a trainer.