I've had 3 different flight sims. I started out with an old version from Dale Brown. It wasn't bad, but it came with a controller that wasn't the best. I then went G2, it was a big improvement. When G3 came out they didn't offer any type of upgrade for previous owners, which I didn't appreciate. I was at a hobby show and saw AFPD being demonstrated and I bought it. I've been happy with it and that's the one I still use. I've only played with G3 and G4 for a few minutes and I think that they would be good also. A friend of mine had the version of FSOne that came with his P-51 and he didn't like it. He's still "barrowing" my version of G2.

I think that any of the ones that are available will be better than no sim at all. So get the best one that you can afford.