I'd say FM in DCS is far better then all others. IL2 is a total joke. I think AH has that beat in that area.
in AH flaps are not nearly draggy enough but nowhere near as bad as that joke that IL2 is.
DCS has several flight models. The standard flight model, SFM. The advanced flight model, AFM. The professional flight model, PFM and the external flight model, EFM.
SFM is mainly used for AI aircraft. The AFM is used for a couple of aircraft, simple but OK. The PFM is used on most aircraft. It's not bad, but obviously better suited for jets than propeller driven aircraft. The EFM is as it say, external. Then it's up to the developer of the plane to define it. This can be anything from OK to complete stupidity. The "best" aircraft from partner developers typically have EFM, because they are then free to do and use whatever they see fit.
As with anything; garbage in = garbage out.
I use the Yak-52 in DCS to train aerobatics at home. The FM is the PFM, and it does a good job in recreating the real aircraft (which is why I use it). What's bad about it is at low speeds, where it behaves like Bambi on on the ice, nothing like the real aircraft. All aircraft becomes a bit "Bambi" at low speed, but it's overexaggerated in DCS. It becomes unphysical. The pitch, yaw and roll moments are all wrong compared with the effects of elevator, rudder and aileron at that speed. The same goes for all propeller aircraft there, it's painful
The other thing is they are modelled to such detail is ridiculous. Some of the gear handles in WWII planes were very unorthodox. Stuff had to be uncaged, then push and hold a button, twist it, etc. All this is modelled. The point is, that fine grade modelling makes zero sense unless having an exact working replica of the handle. Ctrl-shift-h, ctrl-shift q etc etc is
not how it worked
Is it as far from reality it is possible to be. Ok, the mouse can be used, as if that adds "realism"
I have yet to see a WWII fighter with a keyboard and a mouse.
IL-2 is much better in this respect. What IL-2 isn't particularly good at is out of envelope behavior. It also has some oddness here and there, but the overall behavior is physical at all speeds, thus overall the best there is IMO.
AH is not bad at all, and could also easily be used training aerobatics if it had some relevant planes (as could IL-2). A spitfire is not a Yak-52 though
As for the EFMs in DCS, there is nothing to say except garbage in = garbage out. Very few simmers have tried a real F-14, so very few has anything relevant to say.
The funny thing is that X-plane can be used to pinpoint exactly what is wrong with the PFM in DCS. Not that X-plane is 100% correct, but it is the closest we have to a first principles approach, and is always within lets say 5-10% error. The errors in DCS is probably more like 100-200% off at low speed.
Anyway, way off topic
My point is that AH is not bad, it only need some attention. Will it ever get what it needs? DCS is in some ways spectacular, in other ways just plain stupid. The best balance can be found in IL-2 today IMO.