The worst trainer is an aircraft which was never intended to be a trainer, but the newbie has insisted its going to be their first airplane (aka a scale P51 or similar). Yes, I've seen it happen and it is ugly.

At our club field we are encouraging the new guys to purchase the Aircore 40. It's horribly ugly, but will rebound from a crash better than eny other trainer I've seen. It's about as stable as any other trainer I've seen. It definitely needs an O.S. 46FX or equivilant for power. Bought one for my son. Hope to finish it soon.