I've been using FSOne, have never tried the others. I only really care for heli's and for me it's a trainer. So take what I say with a grain of salt.
I like FSOne, I can configure the heli to do anything I want, heavy, light, side heavy, whatever.
I've created new scenes (pano's) and it is more realistic for me this way. I also like the support from FSOne and occasionally get help by Inertia Soft (even though they are not tech support). I don't think I have found anyone more helpful, ever. Remember I don't have any experience with the other companies.
Scott