In regards to current games I only have experience with LoMac and IL2 (if only Jane's F/A-18 had LoMac graphics...sigh). LoMac is actually quite easy to fly. The weapons systems and radar are the biggest challenge. LoMac is graphics intensive, so unless you've got a fairly high-end card you can expect some low frames and choppiness during explosions.
IL2 is much more difficult to fly. Although the aircraft systems are not complicated (guns & bombs pretty much) the flight models are very realistic and it takes a while to get proficient. IL2 will run pretty well on a mid range machine however.
If you're looking for online play IL2 has a much bigger fan base and you can find a game to join anytime of day. The Single Player in IL2 is also exponentially larger and more involved than LoMac with realistic WW2 battle scenario recreations. IL2 also has the Ace Expansion Pack, and Pacific Fighters (with Battle over Britain coming), so IL2 has many, many more possible scenarios and maps to fly on.
If you're looking for an easy to fly sim that you can get your feet wet with I recommend LoMac. The only caveat is that you will probably get fairly bored with it after a couple months. IL2 will be harder to learn and get good at, but the game will be around a lot longer.
You can decrease the difficulty level in both of these games so you can use training wheels while you learn.
Falcon 4 is the king daddy of all time with a steep learning curve. Flying the f16 is super easy, learning how to operate the avionics and stay alive in combat is very very tough. If you just want to fly around and have fun, I love f4.
If you want to dogfight, I'm with squid: IL2 will teach you how to fly (the hard way) and the weapons are simple: there are no avionics to learn.
2 things that will increase your enjoyment of flight sims exponentially:
1) Track IR 3 (with the vector expansion as soon as you can add it!)
2) A good hotas setup. I use el cheapo Saitek X45 but if you have bags of money there are nicer ones out there.
If I could only get one or the other, I'd get a cheap joystick and splurge on the trackir.
Ya, MS flight simulator 2004. i got that a few months ago with a logitech joystick and its fine. ive played it a little but CS:S caught my attention. i go back to it every once in a while and continue with the pratice lessions. I think that would be the one to go with because it has lots of diffrent plane types and pratice lessions and readups on what you will be doing and what you are going to learn. its also got a neat online multiplayer function but i havent used that yet.
Squid, what are you playing now? Maybe that's a better way to go about it.....
I still fly them both off and on depending on the mood. LoMac is fast and furious with rockets and s*&t while IL2 is tactical with more weight placed on how well you can outfly your opponent.
I know nothing about Falcon 4.0, but from the screens I've seen I think all the money I've spent to make my games look pretty would be wasted on it. But, and there's always a but, the people you play with make the game so if you guys get it going I'll jump in.