Depends what you're looking for. If you're looking for heft in the hand, go WE. If you want outright reliability and shooting performance, TM bar none.
TM's hop up design is stellar. You can tell that they put in significant engineering when you shoot their GBBs out of the box. They're also tuned to work decently well with lower pressure HFC134a. That will extend your playing season significantly.
WE gloms on a heavy metal slide that can cycle in the best of conditions, but if things cool down you're stuck. Their heavy slides require lighter springs to cycle because it takes so much work to get the thing moving so they go light on the spring. I've got a WE 3.9" which is pretty much a copy of the Hicapa. The spring is so slack that you can do what I call a "whip cock". Punch forward aggressively and you can cock the slide with inertia. Just like real steel, if you use a light recoil spring and get a little grime or gun smegma and your gun may fail to return to battery. I also find a bunch of goofy little mistakes like springs that aren't quite the right stiffness which leads to fun troubleshooting adventures.
Finally, WE uses single port mag valves.
for an explanation of double and single port mag valves scroll down on this post:
http://www.airsoftcanada.com/showthr...&highlight=ksc
This leads to frequent short fills which would probably be really bad on a singlestacker mag with limited gas capacity. This is the shortfall of buying from clonemakers. You get a sort of parody of what was originally a beautifully engineered device. Some features get duplicated, some mimicked, and most subtleties outright missed.
Has anyone broken a stock TM slide recently? We're all blasting propane now. I'm not sure if I've ever heard of a slide broken by recoil force. I've seen a gun or two pwned by a fall onto concrete but post TM Hicapa slides seem to be propane tolerant now.