Basically, Realflight G2/G3, Aerofly Pro Deluxe and Reflex XTR are the only one which seems to simulate helicopters properly. All other sims seem to model helicopters as a special type of airplane, which does not produce the correct flight characteristics.
The incorrect translational lift model actually affects hovering as well, because real (light) helicopters tend to bob up and down when there is a slight wind. This is because the wind has the same effect as forward flight - it makes the heli generate extra lift.
So, in Aerofly Professional, if you turn on wind, your heli doesn't bob up and down properly - it just slides around horizontally, which is incorrect. Realflight G2 and G3 models translational lift correctly, and the heli will gently bob up and down as the wind gusts. They also seems to model the "rotor wash" effect where the main rotor blades become less efficient when they enter their own rotor wash.
Therefore, if you learn to hover completely in FMS, Easyfly, or Piccofly, you will not learn how to properly use the collective to compensate for the effect of wind making your heli bob up and down. This can be learned later on a real heli, but it will require some adjustment time.
Most simulators have wind turned off by default, which makes hovering unrealistically easy. In order to accurately simulate being outside, you should turn on a little bit of gusty wind (maybe 3 mph or so).
When learning to hover, don't worry too much about finding a simulator which has (say) the Corona. Just learn to hover on the helicopter trainer model supplied with your flight simulator.
Imagine that you don't know how to drive a car and you plan to buy a Honda eventually. Do you really need to practice on a Honda so you can drive the Honda when you buy it? The basic driving skill is pretty much the same for all cars, with the exception of small driving differences and control placement.
Helicopters are pretty much the same way. Some helicopters are smaller and therefore more twitchy and difficult to fly, but the basic skill in flying a helicopter is the same across all models.
One nice feature of Realflight G2 & G3 is the network play, which allows you to fly and chat with other people using Realflight on the Internet. This helps to alleviate the tedium of hovering practice.
Reflex seems to be more processor-intensive than RFG2. There is at least one report that RFG2 runs faster on a P3/500 than Reflex. If you have a machine under 1 Ghz then RFG2 may run better on your machine.
Both RFG2 and Reflex require fairly good video cards to run well. I would recommend at least a GeForce 3, although people have run RFG2 on as low as a Riva TNT (probably with most effects disabled).
A huge number of additional aircraft, scenery and utilities for most of the main simulators can be found at www.rc-sim.de .