I tried FlightGear and found it to be a good sim, but I am just too used to MS flight sims that I didn't want to face the learning curve on a different one.
I tried the demo of X-plane and it was very good a few years back, but I like the graphics on the MS FS's. I may need to check it out again and see if it is any better now that I have a machine that will actually handle the simulation part of a flight sim and not run all stuttery with the sliders pushed up on high.
I would say FSX or FS9. Or even MS Flight when it comes out. MS always makes good flight sims from having used them. If you are wanting to try something new, X-Plane is something to consider. If you are wanting to get a better sim for some reason, wait for MS flight.
No one has mentioned Rise Of Flight here? The graphics are as good as FS9.
I'am just started using B17, the Mighty 8th. That Norden bombsight is neat.
my dad cant wait for that... all prep'd & ready for it.