Hmm, hard question as my GHK isnt stock and has a new barrel and hop chamber/rubber. The MWS is stock. That being said, I think the GHK because of the kick and realism is much better than the MWS and when it was stock it was just as good anyway. The MWS is excellent straight out of the box but if I had to choose I would go for my GHK every time. Though it will be interesting to see what TMs AKM is going to be like - I will probably buy one.
I also prefer the GHK because its a lot simpler to work on the MWS I haven't dared take apart yet.
A better comparison would be the GHK M4 to the MWS, not my AKM