I fully agree with Tex, it really depends on what you want to fly in the future. That is if you are on a budget and you can only afford one engine. If you will be keeping your trainer and buying your 2nd plane with all new gear, then I've heard the bigger the better for a trainer. Easier to see and control. The drawback is that you won't be able to share props or spinners or spares for that matter.

But... on the other hand, I've found that the selection of 40-46 models is multiple times that of the 60-size planes. It's not only easier on the wallet, the choices you are limited to at the 60-size (should you be considering sticking to one lump or one size) may sway you to go 46ax, which, by the way, is the engine of choice :-)