I think the R22 is a little more gentle on the engines. From memory, I think the O-360 in the 22 operates around 2,650rpm, whereas the IO-360 in the 300 is more in the 3100rpm range. (don't quote me on that, but I think it's around those figures)
I haven't done any work on the 300's, but the 22's are a very simple aircraft, and reliable if done right, they will bite if not respected though - pilots realise the lack of power pretty quick on a hot day, full fuel with a tail wind! I've never Piloted a Helicopter, but done some work on the 22's in the maintenance side of things.