Depends on what qualifies as 'better' in your eyes.
From my observation:
KJW is reliable as hell. I own their 1022/KC02 model and its been amazing. Fun unique little gun too. I hear nothing but good things in terms of their M4's internal performance. Though they do look kinda crappy externally, with a strange finish to the metal and some reports of a more brittle metal used in the receiver. A friend down south says his receiver is starting to crack a little at the neck of the gun, between the delta ring and the receiver itself. He cradles that thing like a baby.
As for WE. Externally, they're beautiful, wide selection of guns and bear an excessive amount of aftermarket parts to chose from.
Thats for a reason, though. Depending on the gun you get, you'll find little quirks in the building materials that WE mysteriously decided to cheap out on. The AKS74U having a very cheap pot metal for the trigger mechanism parts. Or using a brittle plastic for the loading nozzle rails on the M14.
Overall, if you have a deep pocket full of money, WE is the way to go. Once you have the rifle built (Think of their stock guns like a shell) the rest falls in within a reasonable price. 40 dollars for a magazine is nice, compared to the 70 or so that KJW costs.
Either way, Both are good. Just weigh what you feel is more important, and what you're more comfortable investing in.