I've owned and played with all the airsoft Sig P226s apart from the WE and the KSC (and the Inokatsu, but who's going to count that anyway?) and I wasn't very impressed with the longevity of any of them tbh.
My first pistol was a KJW P226, and it was amazing when I first got it, but in barely 6 months the performance had dropped right off to the point where it was useless even in summer weather. No doubt this could've been sorted fairly easily but I was a total noob and had no idea what I was doing, so aside from field stripping it I ended up selling it on to a mate because I couldn't rely on it anymore.
The KJW magazines are also utterly terrible, if you do go for the KJW, then make sure you buy TM magazines for it.
The TM I had, I bought second hand and it must've been about 8 years old. The performance was about the same as the KJW, so that was highly annoying, but I'd put that down to the age. I bet brand new ones are probably pretty kick-ass; the issue with TM is that they're a bugger to find, even buying a second hand one took me about 4 months to track one down but on the swing side they have the most parts available because companies always seem to scramble to make TM replacement and upgrade parts.
A mate of mine has the KWA and it really feels terrible, it has a really random blend of metal and plastic parts and I just dislike everything about it. It's also the least fun to shoot and from my experience shoots the worst. It also sounds like it's running out of gas all the time because the slide is very light so it doesn't take a lot to cycle it, compared to the others it sounds a lot punier. Considering the cost being higher than most I wouldn't even consider the KWA, despite the supposedly better cold weather performance and superior build quality I just didn't see those things in it at all. Feels horrible, performance is average at best, costs a lot = just pretend it doesn't exist.
So what's left? The WE which I haven't tried, but my WE Glock has been the best pistol I've ever owned, so I'd imagine it's of a similar quality and performance level as that, I've not heard anything bad about them either.
If I were in the market for a Sig, I'd probably get the WE. If I were to rate them in order of preference (not performance or anything else, just which one I prefer the most) it'd be KJW/TM/KWA in that order. Obviously I've not tried the WE so I can't really place it, but I'd put my Glock first on the same list so assuming the Sig is the same, which I do, that's the one I'd go for.
The WE is generally the cheapest too.