KWA has a proprietary-ish gearbox. its a modified V2 gearbox so even tho they are decent once it breaks depending on the part you would have to go back to KWA for parts. also their externals suck compared to VFC and G&P imo.
TBH you wont find anything amazing stock out of the box. i mean they will all work for sure it just depends how long before you need to replace a part. They WILL break sooner or later just depends how soon. Unless you encounter a Lemon in one of the internals of the guns, VFC and G&P should be able to go through a couple thousand rounds before anything serious starts to happen. I mean even for KA, I'm not sure about the imported ones that you get here, but the Stock KA Larue M4 i got back in Hong Kong Lasted about 3 different days of gaming before i stripped the piston. and that was running on a 11.1V 20C lipo too
so it all depends. you will deff get a couple games out of the box with those guns it just depends when its going to break