If you go with the KJW version, you can use TM parts. Not all parts that are "TM Compatible" are made by TM, nor are all TM parts superior to the aftermarket parts. Depending on the part you want, you'll need to do a little research. There's not too many brands though.
If you want realism, KWA is the most realistic, as far as airsoft guns go. Their M9s are called "M9 Personal Training Pistol (PTP)". It boasts "Realistic construction and field stripping". To be fair though, most most M9s field strip the same as a real pistol, but getting into the guts of it (trigger assmebly, etc) are obviously a bit different than a real one.
From the sounds of what you want, KWA would be best for you. Buy it, play a season with it, try out a TM M9 at a few games for comparison, and see how it goes. By the next year, you'll probably figure out the shortcomings of the KWA, and you'll be able to do some research to see if TMs suffer from that problem, and/or if there are aftermarket parts that fix that problem that are NOT available with KWA (aka KSC).
I guess a very simplified way to look at it, is you should go with KWA for realism, or TM for exceptional reliability. You could also go with KJW for a gun that has the TM aftermarket parts for easy fixing for reliability, and full metal to make it more realistic than TM, but has no functioning decocker.
KWA is not poor quality, though, so while the TM could be considered more reliable, it's not to say that KWA is not.