Robert,
Because you are US based, unless you are very wealthy, 99% of the available helicopter training aircraft available to you are going to be Robinsons. As you've no doubt determined, there is the odd S300 or old B47 around, but those are comparatively few and far between.
AFAIK, there are no G2s anywhere near you, and only a handful in the US at all.
So...you are going to almost certainly wind up in an R22, or maybe an S300 if you are lucky to have one about. You could pay around twice the price of an R22 per hour if you'd like to learn in an R44, assuming there is a school that is willing to teach that way (some are). Because R44s are less plentiful that could lead to aircraft availability issues.
If you are, again, very wealthy, you could possibly find someone willing to teach you in 206 or something like that.
The other thing to consider is what track you are on. If it's a personal/private owner type track, then it probably doesn't matter what you learn in. If you are on a professional helicopter pilot track, then that normally means time in the trenches as a CFI. Again, since 99% of all US civil helicopter training is in Robinson products, then Robinson time would seem to be more valuable.
aa