Il2: Your head is attached to pilot seat
Ah: You have a 3D cockpit
Il2: just mission or short campaings
Ah: You get the feeling of a war in course, helping your country, your actions will pay for you country
Il2: number of players are low in each server
Ah: you get high number of player in an arena, so you will see bombers, transports, jabos..., things that you will not ever see in an Il2 server
As far for an online sim, those are very big differences to choose one or another.
None of them have relation with the game per se, just the kindo of game they are, boxed or online game
(boxed game, few players= better graphics)
(onlineGame, more players=not the great graphics, but better overall game because, it is in continous development(flight model, game improvement, options...))
If you entry in the game:
Just my opinion, Passao