Most clubs will give you orientation flights, that's the best way to begin to decide on a trainer. Finding out which one's your LHS stocks is important too. Like that say on TV, NEVER buy an RC that doesn't have spare parts available for it.

I'm not sure how you make an objective selection. Some are bigger, some are coroplast, some wood, some are slightly more aerobatic.

My LT-40 has a 71" wingspan. I've found it to be bigger than most other 40 sized trainers, yet it still takes a 40 sized engine. Bigger is important, cause they go out of sight pretty fast.

A .60 sized trainer is probably going to be more expensive (bigger motor than a 40 sized).

I also think you should PLAN that your trainer is a transition to a sport model. Then you can concentrate on the simplest set up for you.