The TM hopup is faaaaar superior in design, and very slightly superior in performance. I don't know where you heard KSC internals are finicky though, they're very reliable and sturdy, with the exception of maybe the floating valve (easily replaced with readily available metal ones) and the selector on G18Cs.
If I were to buy a glock for the first time (again), I'd take the TM unless I wanted long mags (which, I suppose, is just a matter of time).
This might help:
http://www.arniesairsoft.co.uk/forum...455&hl=\glock\