Talking of FS9, the PMDG 737 from 2005 (?) never convinced me. PMDG's 747 however was excellent, so is Level-D's 767, which before (FS 2000 + 2002) was called Wilco's 767
Pilot in Command. If there is a classic addon of a high-quality airliner with a long-running tradition in the FS-series, then this 767. It even is available for FSX, and like the thre times before it scored ecellent reception. Transformed into 4 different versions of FS, since 2000 - not many planes out there with such a record. Realair's SF.260 SIAI Marchetti "only" saw 3 incarnations, if I do not miscount it.
Currently exclusively using the iFly 737. Very very good. Just that the new PMDG 737 looks much better and has even more system depth. "
Even better" is the enemy of "
best".

iFly needs to rework the HUD, though, it looks not good, and very blocky in fonts.