H&K Mk 23? Uh....
As much as I love H&K pistols, the SOCOM was less than a hit even in the SpecOps community it was tailored towards. The civilian version shares all the drawbacks of the SOCOM while having none of its benefits. The Mk23 is heavy and very large. It is accurate and sturdy, but it only has a very limited application range. If you're a combat frog (SEAL/UDT etc.) the suppressor built for it in combination with the slide cycle lock would come in handy, but the suppressor is not available to civilians anyway. The SEALs and other SpecOps folks figured out quickly that the gun was intended for work more suitable for a suppressed SMG, and its size is a direct result of that. They went back to their SIGs and M9s, and as far as I know the SOCOM is not much in use these days. It's half the weight of an MP5SD, and almost as long when you attach the suppressor.
The Mk23 version for civvies has little practical use, and very limited appeal to non-collectors, due to its unsuitability for CCW and its staggering price tag. A USP Expert would do the same job in a lighter and less expensive package.
If I was back in the service and preparing for a night exercise/operation, I'd grab an MP5SD and a USP off the gun rack before I let them hand me a SOCOM brick.
Ok, off my soap box, and back to other polymer guns...Glocks are probably the best combination of durability, ease of use and reliability out there. H&K USP is very nice as well, but a tad hefty in the full-frame size. The Compact would fit the bill better and is highly modular as far as triggers and decockers/safeties go.
I picked up a SIG Pro SP2340 in .357 SIG two weeks ago, and it is a sweet shooter, maybe even more durable in construction than the Glocks, and inexpensive to boot. I'd give that one a shot, since it can be reconfigured for lefty use, and it has a nice wide slide release that can be operated well even with the non-dominant hand.