he best trainer now is the R44 as with two up it has no fuel load limitations and is totally representative of modern helicopters. Obviously the ideal is to go straight to the 206, but is seriously expensive.
I've taught in R22/R44/R66/B206/B206L/F28A and I would say if it was my client asking about training I'd go with the R44. Now, I may be a bit biased because the school I currently teach at has R44s, but let me give you a few reasons I think it's a better idea than going direct to the 206 or using the 300.
First, let's talk about teaching in a piston vs a turbine:
1) Less chance of smoking the engine during start. Yes, they eventually need to learn to start the turbine, but arguably smarter to do this during transition when they have a little more experience under their belt. I might feel this way a bit because the first 206 I flew had a lousy battery and every start was exciting!
2) Instant throttle response of the piston is pretty nice for a primary student who is still learning to control the aircraft and hasn't learned to think ahead of the aircraft a bit. It's also nice for the instructor fixing the student's mistakes. It means the instructor can let the student go a little further before he needs to get on the controls - he doesn't need to be quite as conservative when it comes to engine management.
3) I would say the limitations of the piston are more forgiving than the turbine. Not only temp and torque, but having to watch 3 power gauges instead of 1 increases the workload of the student. Again, they do eventually need to learn it, but when they have 50-60 hours it's a lot easier than when they have 5-6...
Advantages of the R44 vs the -300 or R22:
4) With the boosted controls the R44 controls feel very similar to the 206. And of course you can teach boost off with the R44.
5) The R44 flies more like a 206 than the smaller machines. The response of the aircraft due to it's slightly larger size is much closer to a 206, the larger diameter rotor feels a lot more like a 206 coming out of confined areas, and the power available is closer to the 206.
6) Unlike the -300, learning to hover the R44 prepares you for hovering the 206. The response (especially to a new pilot) of a two bladed is quite different than an articulated system (the -300 is easier, so you could make the case that teaching in the -300 will make it easier to learn to hover and then the pilot can get used to the dynamics of a teetering system during transition).
7) The R44 speed is more in line with the 206 than either the -300 or -22. With just hover power settings you can be doing 100 knots on downwind. It's a very clean fast machine in the pattern.
8) Hover autos and touchdown autos are much closer to the 206 than either the -300 or -22. Well, hover autos in a piston are never going to be like in a turbine, but you have quite a bit of inertia for the hover auto in the R44. Touchdowns are a piece of cake - very similar to the 206 but with the advantage of being able to power recover at any point (seriously - at 12 inches with 70% RPM you can crank the throttle on and avoid hitting the ground if it suddenly starts to look bad).
Other benefits to the R44 vs just training in the 206:
9) You won't bang up your nice 206. Nobody will care if you bang the R44 around a bit! :-)
10) Probably cheaper to insure the R44 for primary instruction than the 206
11) In the USA significantly cheaper to operate, but that might not be the case elsewhere.