I wouldn't even bother with FSX or FS9 if you're not serious about spending *hours* navigating, reading instruments, flying mundane routes, and practicing your maneuvers. Personally, I love that kind of thing, which is why I love flight simming. I can spend hours simply flying a small WWI fighter around France, or even a large modern aircraft across the Atlantic.
As far as X-Plane goes, yes, it does indeed have its merits - and it's a very good simulation - but MSFS is far from unrealistic. It never has been marketed as a 'game' and, as such, has never been plagued with severe dumbing down and fudging like in so many 'sims' in the sim-racing world. I wouldn't say that the X-Plane/MSFS sim-divide is obvious - they both have fantastic merits, and unbelievable drawbacks.
There is little merit in any realistic flight simulator unless you are willing to just sit for hours doing relatively nothing, just because you want to clock up flight hours and experience. Payware addons like FSPassengers add a lot to the immersion factor of passenger flights (both modern and older), but require a lot more skill.
Don't expect to be having lots of fun flying around on MSFS or X-Plane if you're not willing to take it at least half as seriously as real aviation. Otherwise, you may want to go and play a flying 'game' instead.
As for controls, well, your keyboard *can* suffice - but I'd strongly recommend against it. At the very basic end, any old joystick will do - but ideally you want a very sturdy, robust and precise set of tools. The low-end of stuff you're looking at (minus rudder and a proper flight-column) is something like Saitek's X52 (or X45 if you can still find it) - though these are better suited to sims like Falcon 4.0 and LOMAC (for obvious reasons).
You'll also want to be looking in the direction of some quality addons (there are some top-notch freeware ones, but for the absolute quality - you want to go payware... things like SSTSIM
are very well rated in the dedicated FS community). The default planes in both MSFS and X-Plane are lacking in those details that make the flight-simming experience perfect (things like nicely detailed VCs, etc). That's an obvious side effect of something being shipped with a product like this.
Don't expect to have a nice banter with the ATC in either sim, they're very limited and are honed for near-perfect route-based flight. Of course, you can always fly VFR... but where's the fun in that for anything over the size of a King Air? There are some ATC add-ons for MSFS, and apparently some do some good stuff (but I haven't bothered - as the normal ATC doesn't interfere with my flying).
Basically, if you're looking for civilian and commercial flight-simulation, you want MSFS9 (or X if you feel like risking it) or X-Plane. If you're looking for realistic combat sims, there are only two options here... LOMAC or Falcon 4.0 (For LOMAC you'll want Flaming Cliffs addon, as it's essentially a huge bug-fixing addon, plus a new plane, to correct the state of release when Ubi forced the release of LOMAC early).