Althought i prefer the historical ones (vietnam and israel):
I haven´t played SF2I, and i wish i had. Arab-Israeli wars are quite balanced and the variety of situations, missions and weapons systems found make it worthy, i hope i get it eventually
SF2V has many limitations in its timeframe (15 years) and the variety of aircraft you can put inside, also the fact of never having the chance to play air defence against red air, but an excellent point are carrier ops.
I guess that I don´t fancy the over-fictionalized in SF2 Paran Dhimar, despite i got SFP1 and it allows you to do whatever you want, with the aircraft you wish and whatever the timeframe.
My vote goes to SF2E, because of the so wide beam of years covered (the 46 best years in military aviation advancement!), the lots of materiel included (NF4+ made it a totally different game) and to a less extent, the "red dawn" like feeling of an hypotetical modern war on our western, first world, the way it was expected to be and never happened