You'll get various answers, from "R22's are deathtraps" to "Bell 47s are too old".
There's no right answer. Sure, the Bell gets you used to working the throttle all the time as there's no governor, it's got more rotor inertia so autorotations are, I'm told, easier. But it's a sloooow cruise machine - not important when training, but once you have your licence it can take longer to get where you're going.
The R22 is quicker (I think), autorotations are definitely much more exciting, there's loads of them about, and generally most of the problems are well documented (as on the Bell) so if you read up and are well taught, there should be few surprises.
Best bet - take a trial lesson in both, preferably at the same school, and see which you prefer.