I have only tried two sims FSOne and G3.5 and G4. FSOne has the physics and G4 has the entertainment. Either one is going to improve your abilities.

FSOne can be difficult to set up correctly and has no where near the plane inventory.
G4 will never fly as true/well as FSOne can.

G4 also requires an extrodinary computer to run on all high settings with complete water effects.
FSOne just dropped their price to $99 and is marginally questionable long term.

I was lucky on FSOne setup as I fly an Ultrafly ultimate and as soon as I scaled the plane correctly (turned out to be a 66" wingspan when actual is 33" off the top of my head) it was amazingly accurate. By that I mean that I scaled the plane until it flew like my ultimate. The real fun began when I went back to the real thing and I was able to Harrier land without thinking about it in front of a group and do some pretty cool semi rolling harriers. When I switch back to G4 it is too easy to fly compared to real life.

Did I mention that G4 graphics are insane on high settings.

FSOne is marginal with helicoptors.

Your choice- great computer game with better helicoptors or great plane simulator.

I have setup G4 on a true gaming machine and playability(graphics, multiplayer, water landings and plane choice) is hard to beat. If you are into computer games, focus on helicoptors and have a current top of the line Core 2 Duo machine with ATI 3870 or better graphic card, knock yourself out with G4. Otherwise, I would save the money and get the (IMO) better simulator- FSOne.

As a side note G4 responded performance wise to the video card (GPU) while FSOne was processor (CPU) driven for given frame rates.