Well, let's see......
There's a lot of different engines and drives to choose from. Your typical 2 stroke, in frame type of engines are pretty generic, so you'll want to choose a vendor over a brand.
As far as four stroke, rear-or-in-frame mounts are concerned you'll be able to choose brands. Some of them will be familiar names.
It would be hard to suggest one type over another for you. But I will say that if a motor assisted bicycle appeals to you, then you should take the plunge. At least 9 out of 10 people, it seems, end up saying, "Why didn't I do this sooner?"
The best thing you can do right now is to start reading the threads in this forum. Click on anything that has an interesting looking title. Keep reading and before you know it you'll start to form the idea of what sort of engine/drive you want.
Have fun.
