Thats an interesting question but since this is the beginners forum the responses might not be as numerous

Me personnally I've flown/Fly sport models low wing high wing shoulder wing but I always try to have a trainer in flyable condition.

As far as progressing in this hobby I think to much emphasis is placed (here and at the field) on moving to that "second" plane and alot of the modelers I've seen really haven't "mastered" the trainer yet but prouldly bring out that second plane and begin to develop bad flying habits...

My question to you is when does one "know" that its time for their second plane.. And please don't say after crashing the first