As an actual skirmish weapon the WE MP5 GBB is much more serviceable than the VFC. The VFC has a bolt carrier made of cheese which will break if subjected to a few HK slaps (there is a Badabing video on this, but I also have some personal experience with this with a friend who got a VFC MP5 having seem my WE one). The VFC also has a really rubbish mechanism to stop firing when it is empty, the magazine follower basically blocs the bolt going all the way forwards so you cant shoot after the last round fires. The WE suffers from neither of these issues.
On the plus side the VFC has proper markings and really does feel lovely (its only once you hold the VFC that you realize how cheap the WE plastics feel, I thought my WE was nicely finished until I handled a VFC).
The WE does have a couple of problems. The small part that actuates the dead mans click on mag empty is fragile, the flat spring that limits the 3 round burst can break and there are reports of the hammer breaking on extensive use. I have personally experienced the fist two issues but never had a hammer break. For all of these issues replacement parts are readily available, easy to fit and so cheep you can easily order an extra one or two and carry spares if its something that bothers you.
If you really must go GBB and you actually want to use it rather than just look at it and stroke it occasionally then I'd go WE, and I have put my money where my mouth is on this one as I have 3 WE MP5s in various configurations. If the authentic look and feel and proper trades is more important to you then the VFC is the obvious choice.
I Can't really say much about the Marui NGRS, I have had a play with one and it was nice, but I didn't really subject it to any serious use and it didn't tempt me to sell my WEs. However as a general rule AEGs are much less maintenance and cause less aggravation to use than GBBRs. As said above the real MP5 is a very soft shooting gun (one of its major appeals to special forces when using the sling brace method) so the NGRS recoil isn't that unrealistic.