I agree with Jesse on this. Go as big as you can afford. The 500/550 class is a perfect start if you can afford the parts.
I would suggest you get extra parts at the beginning before you fly. This will ensure that you get back up right after a crash.
Good luck.
These guys have it nailed, the 450 is a great heli but can be twitchy as hell, the larger heli's have alot more stability due to the mass of the rotor disc as compared to the smaller 450 class,
If I had the extra cash when I bought all my kit I would have gone for the 500 class. And what the guys at the club said about going for the one you want to end up with, dude you will always want something bigger or better.........
But guys this is off the thread topic so you / we need to take this somewhere else, we don't want to thread jack.