I own and fly them both. There are select aspects in which Il2 betters AHII, perhaps, but not many. Il2 has managed to stick every WWII airplane imaginable into their lineup, which is impressive, but it gets just as many details wrong as AHII, if not more. AHII certainly has a more complex flight modeling; Back when I had my old computer, I was running Il2 just fine on fairly high graphics settings I wouldn't even have attempted to use in AHII. The extra computing power AHII sucks down must be going to the aerodynamic calculations.
Mainly what kills Il2 in my mind in comparison to AHII though is an awful viewing system, unless you happen to own TrackIR, the bizarre instability of the aircraft, and the a-historically impotent nature of the weapons, especially .50s.
If I want to look at some pretty scenery and hear some nice sound effects while popping a few AIs, I boot up Il2. If I want some real chess-game ACM, I start AHII.
Once you get used to AH Nonaste, you'll be doing ACM, especially out-of-plane ACM and Energy fighting, on a level that is practically impossible in Il2, owing to the viewing and shooting difficulties of that sim.