Never forget the second hand market, there are tons of very nice helicopters for sell normally, and often they very nice bargains.
Good old Raptor 50 is till one of the best learning 50's. Parts are reasonable and normally easy to find.
I'm not going to class heli's in advance/intermediate as most helicopters can fall into both. Change paddles and head settings/radio settings.
450:
Beam E4. Extreamly stable machine and very precise. Not as twitchy as trex's so bit easy to learn on. (also makes excellent learning machine) (
www.beamheli.co.za)
Trex 450: Very twitchy machine. good for hard 3D flying, but don't expect any neat flying, its simply not precise enough: (
www.align.tw)
500: no clue, never flown any 500's.
600/50 classs
Compass knight 3D: One of the best 3D machine still. Simply fly's amazing. Company not the best and parts you need to import yourself. (
www.compassmodels.com)
Outrage 50, Very nice machine. Feels very light in the air. V1 got few bugs in them as most new heli's has, but knowing outrage, the'll get sorted quick.(
www.helidirect.com)
Raptor 50 SE: Very very nice machine to learn on. Heavy and exreamly stable. Make you'r flying look so much better

(
www.thundertiger.com (i think))
Other makes I cannot comment on, not flown them myself.