It all depends on you priorities. I consider my .45 4 stroke to be very versitle. I just put it on a .25 low wing plane. A while ago I used it on a plane with floats. Can also mount on a bunch of different high wing planes such as a Piper Cub, etc. I think it's a great size. I also consider a .25 2 stroke to be very versitile. If I put it in a quick .15 size plane, I have a little rocket. Mounted on a standard .25 size, can run all day on little fuel. In case you haven't noticed, I like small planes. I've got two in flying condition right now. I can put them both in the back of my truck, with the wing on. Needs no assembly or disassembly at the field. Others prefer larger, or smaller, engines. If I built a rack for the truck I could probably get 4 or 5 .25 size planes in there.