In my mind:
DCS : best accurate FM and full real clickable cockpit. but worst DM effects and not full server abbilities and no WWII object map and immersion, no bombers to shout down. A study Sim.
the one I play most at this time, but waiting for Edge 2, a WWII Map, and full server with +100 wwii warbirds ....
IL2 CLIFF OF DOVER + Team Fusion patch : Best Eyecandy photoreal cockpit and best DM engine. ( no predictable or never the same issue, detailleds effects on fuel tanks, on flaps, rudders etc ... )
nice immersion and Full server abbilities up to 120 players on real size Channel Map ... with no lag for me and 60 fps...
FM quite good in flight ( predictable aircraft when you know them) , not as good, in ground effect / landing / take off.
IL2 BOS : very sensitiv (over sensitiv ?) FM in ground landing. not Accurate FM in flight, but quite good (some needs to be upgraded). Cockpits, colours and graphics looks sometimes In my mind, "old school" or cartonish. except for Zeus user made map wich is nice. DM are not so good (the game seems to only counts the number of hit before the wing fall ...) . Multi player looks like In my mind to much arcade or WT. You must love snow white landscape ... / Unlocking system of Bonus and skins with the SP Campaign can be a problem for MP fans.
No Sim is perfect at this time. But all have some good features. So .... grab them all as I did !