KJW is nice, it's almost the same weight as the real P226 when you've got the mag in.
It's compatable with TM parts, so should you want, you can replace pretty much all of the internals of it with TM.
Works really well. It can work in winter, but don't be alarmed if it occasionally squirts gas everywhere. It's only ever done that to me once, when it was -8 all day, and even TM and KWA pistols were venting that day.
The cybergun/KWC P226 X-5 is brilliant, the only downside being it's based on a competition shooter's pistol, rather than a 'real' P226 (the X-5 is effectively SIG-Sauer's version of Lara Croft's special USPs). Nice, meaty pistol, firm and solid action, and you can get a lot of rounds out of 1 CO2 bulb even in winter. (I've managed 56 shots on 1 bulb, that's 3 and a half re-loads, in -8 weather)
WE - all I can say is that it's cheap to initially buy, but it doesn't use TM magazines. Other than that, I'm clueless, I've yet to find any reviews of WE's SIG line.