I have the iFly 737 NGX and I'm very happy with it now. When it was first released they tried to be supper realistic and modeled the RW feature that if you moved the stick/yoke the autopilot would automatically disengage. This drove most people crazy (including myself) because the least little touch of the stick would disengage autopilot. Since most sticks have tophats to pan the cockpit and outside, you are always touching the stick. However the latest patch resolved this issue and the plane flies very well now.
I just saw the 737 cockpit video preflight check posted by David Freeman and the iFly cockpit is very accurate. I fly mostly using the VC and all the switches are functional. I don't have the PMDG so I can't provide a comparison. All I can say is I'm now very happy with my iFly. Only negative I've seen is a slight hit on FPS.