I've only flown the R22, with a quick half hour in a 300 to see what it was like. My observations :
R22 pros - cheapest, most numerous training heli, agile, easy to fly, "if you can fly a Robbie you can fly anything", governed ERPM.
R22 cons - can bite the unwary / stupid if allowed but the same's true of all helicopters ( low G, low rotor inertia ), low MAUW restricting options, slow(ish), cyclic position/design for tall people like me can cause extra nause getting accurate flying.
H300 pros - not an R22, proper cyclic with working ( after a fashion ) trim, rigid head, more useful load ( I think ), bigger inside.
H300 cons - slower than an R22, more expensive, manual throttle control ( this depends on your point of view ), P1 sits on left which means swapping hands on cyclic to change radios, altimeter settings and the like.
Really it's a suck it and see job. Speak to local instructors on both types, if possible fly a few hours in both looking to see which you feel more comfortable in, and go from there - check first that the hours you do in one will count to your licence should you decide to fly the other type full time.
Is that a tad more helpful ?