I'm gonna say strike fighters cause as far as I know it actually works. Unlike what i've heard about Lomac...
If you get LOMAC and Flaming Cliffs, everything runs nice and smooth. I've had it since May or June and never had a problem.
The difficulty is scalable also, you can set easy radar and things like that so it leans more toward the arcade side if you want it to.
I can't say anything about Stirke Fighters though, I haven't tried it, though it does seem to be a bit more customizable.
Also, it depends on what you want to fly. Strike Fighters is Vietnam era (i.e. F-4, etc..., although you might be able to get add-ons) and LOMAC is more Modern Day to near future (F-15, A-10, MiG-29, etc...).