Moped Army

I've got an oportunity to pick up a used Tomos - sorry, I've got no idea at this point of the exact models or years. I can get one of the pair for $150 canadian (that's like $90 US)! But my buddy will only let one of 'em go. He got them used at a flea market a couple of month back. They both run fine. My big problem is which one. I am told that one has the A5 and the other has an A3 engine. I haven't seen than to verify this yet. I have heard bad things about one of these engine model but I can't remember which one has the problems (or is that which one is quite good?). What are the prime differences between the two engines? Assuming both were in equally good shape, which would be the better engine choice? How do these compare to the A35? Sorry for all the newbie questions, but I've never had any dealings with a Tomos, just my Batavus.

Thanks.

Richard