There's actually something along the lines of five different SOCOM's

Most common being:
KSC's Blow Back Version (early)
KSC's 2005 Blow Back Version Hard Kick
KSC's new 2005 Blow Back Version Heavy Weight
TM's Non-Blow-Back (This one comes with the suppressor and the fake LAM unit, the real one costing a ridiculous ammount of money)

As far as cost, the TM's NBB Socom would probably cost the least if you wanted to use propane as a primary gas source, since it doesn't have a slide that blows back and can break. You'd just have to deal with a horkin' huge pistol (and the cost of getting that holster like gypsy pointed out). And the possiblity that your FPS could break the XT 350 FPS limit. Plus a heavy/long trigger pull (compared to your average gbb) which could affect your accuracy.

This is compared with the TM P226, which is pretty to convert over to propane since the cheapest slide/metal barrel set is 100+ USD, which is a bit pricey, but most likely worth it. If you're content with duster gas (which is easier to obtain now that there are two different duster adaptors for sale) it'd probably just be better since you can crack off shots faster, and get some decent accuracy.

But I suppose it somewhat comes down to style and what type of handgun you want, if you want a really mean/imposing pistol, the Mk23 would probably be best. For compact size, and for that unique JTF-2 look (IIRC they use it, either that or the P228) or for a more tactical look (or if you have any accessories that require a picatinny rail (sp?)), pick the P226.

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