Mmmm.. having flown, and taught extensively in both...
The 300 is easier to fly, but crap for going anywhere as it's SLOW and you can't carry anything, and it burns more fuel. And they always seem to break more often, not major stuff, just niggly things that keep them on ground much more often than the R22. If you want a career as an instructor, then opt for the R22, as Schweizer FI jobs are few and far between.
If you learn to fly on the 300, then when/if you transfer onto a Robinson, you will struggle to fly it as well. Most people I have taught need about 10 hours conversion, and even then, they aren't too comfortable with it, because of the teetering head 'feel', t-bar cyclic position, and RRPM control.