so... you've now proved only that 1) Simulator fans are clinging to Falcon 4 THIRTEEN YEARS after it was made, which would indicate the F-16 remains a popular subject for simulation, and 2) Simulator fans are pouring huge amounts of effort into an attempt to keep a decade-plus game relevant , which is a pretty good indication that THERE ARE NO COMPETING PRODUCTS OUT THERE.
The fact that there are tons of forums for F4 mods doesn't mean the market is saturated, it means that there are tons of forums for F4 mods.
That said, I'd be plenty happy with any number of different aircraft, but I'd prefer an F-16. I'd love an F-15E, but I think the AI backseater route would leave much to be desired, and while you could "hot seat" swap between seats (or even do it all from the front; if I recall, both seats have access to all the systems), you'd be severely overtasked and it would degrade the true effectiveness of the aircraft.
I'd certainly settle for an F/A-18, though I've always thought it was a pretty hideous and hideously lackluster aircraft. I'd be very unhappy with the F-14 due to it's rather one-dimensional mission/purpose (heck, even an F-106 would probably be more fun to play... at least then you get to play around with obscure technology... like nuclear A2A missiles!). But I'd even be more than happy with an F-5E (no, I'm not missing a digit. I mean the lightweight fighter), F-105, F-8, Gripen, Eurofighter, Tornado, Jaguar, etc. Rather stay away from Russian aircraft, because I like my aircraft to have avionics. And the A/C in Russian use are NOT the super badass cool guy new models... those are export-only by and large. I guess the Su30MkI would be kinda neat... but I'd prefer something western.
And if you can't tell, I think a light fighter/attack aircraft would be fun. F-16C followed by MiG29? Roger. Jaguar/F-5E paired with MiG21? Awesome.