X-Plane is pretty good. The scenery is a bit lacking unless you download upgrades. The flight physics hold well until you try a loop, during which the game actually locked while flying the glider. For the detailed panels the instrumentation is brilliant; you can see small changes in readings much better than in FS2K
As for X-Plane, wait for version 6 as that'll be around fairly soon. As for FS2k wait for the 2002 release coming out soon as it offers much over the current version; i.e. doesn't run like a dog on ANY PC you load it on, thats if CFS2 really does use the engine to be used by FS2002.
Hope this helps. Sims are great for instrument practice/learning, heard that many times.
SS