For civvy stuff then I'd go FSX, particularly with some of the addons like REX and GEX. I've not seen enough of X-Plane 10 to comment on this, X-plane always looked good but I found my version (8) not very user friendly.
For military stuff, definitely RoF, and if you've a lot of time on your hands then the DCS stuff is sublime. It's great but it's definitely not a 'just jump in' sim.
Also, for any flight sim TrackIR is a must - but only if you can't get FreeTrackNoIR working first. Seems daft to pay for something when something very nearly as good might work. It didn't for me so I got TIR and it makes cockpit life sooooo much easier.
Check out this sticked thread in the
Helosim.com and Flight Sims section -http://www.subsim.com/radioroom/showthread.php?t=115971
