I learned on R22s. Most of my hours are in R22s. I instruct on R22s...occasioinally, at least.
I had one hour in a Bell 47, and B47 drivers now have my eternal respect. Jeez, it was hard! Under-powered, no governor, ineffective correlator, no low RRPM warning light. How do you hover with half an eye on the instruments all the time? Oh, I see, you don't; you learn to listen for the slightest change in RPM...right, I'm a helicopter pilot; I'm supposed to be able to do that aren't I?
OTOH, if you put a B47 pilot in an R22 for the first time, he'd probably think it was skittish and difficult to control. I suppose it is, till you're used to it. But then, every new type is difficult at first. I had trouble the first time I flew a B206; felt like I was supposed to do everything in slow motion.
So, I'm not an expert, and some of the real experts on here may answer you. But my feeling is that it doesn't matter that much; you'll learn different things from different helicopters, and they're all useful in the long term...the real longterm, lifelong learning experience that is helicopter flying.