Granted, if you can learn to fly the R22, and learn to fly it well you should be able to fly anything. But the 300CBi is a far superior machine. It is a much more stable helicopter, which will help to learn the tricky art of hovering, and I believe a student will go solo in a shorter time in a 300. It is a much more forgiving helicopter, Vfrpilotpb is 100% correct, every helicopter has to be treated with respect. With the fully articulated rotor head you dont have to be concerned with "zero g" situations, something when you have more time under your belt, you will be better suited to recognising and solving the problem. And 300's are not restricted to wind speed and gustiness. Also, the 300's, the C and CBi models are injected, so we don't have to worry about carb icing problems, as Whirlygig said.
I also think they are a much sturdier airframe then the R22.
But before anyone says, yes I do have R22 time. But with about 750hrs in the 300 I prefer them by far to anything, except maybe a nice turbine machine.
Hughesy