first welcome to Combatace,and now to your question...theres so many different opinions on this..for total realism..hands down Falcon 4:AF i mean clickable cockpits and all those radar modes..it's about as real as it gets without sitting in a F-16(of course theres the easy settings),for a prettier sim but not nearly as real theres LOMAC...great eye candy,and some really cool jets.then theres the "light"sim Strike Fighter:project1,Wings Over Vietnam,and now Wings over Europe:Cold War Gone Hot,these are not nearly as real as the others and they are not meant to be...TK is continuing support of these titles,and theres so many add-on aircraft,terrains,and different mods around for them,check the downloads section here.If you want WW2 then theres only 1 choice..IL-2 and ALL of it's add-ons,if you want to be a prop jock thats the only one worth having.
Hope this helps some.