Here is the wiki list of manufacturers.
http://en.wikipedia.org/wiki/List_of..._Manufacturers
Its not terribly detailed, but it gives you an idea. G&P makes decent quality AEGs as well as G&G. Some preventative maintenance maybe required sometimes, just something simple like reshimming. As for KingArms, Ive only ever dreamed of owning one of their premade guns, I have an M4 I built myself entirely out of KA parts and its run very well. The only tid bit I can say about them is that for the most part there externals are better than there internals.
KWA seems to be the new craze, personally it doesnt really ring my bell, Classic Army has come a long way, they have improved their QC for their guns. JG has also come a very long way as well, their guns although plastic like TM run a decent FPS out of the box and may only require a little reshim and metal bushings if even to keep running efficently. Another brand to look into perhaps would be Echo1. Echo1 from atleast how I understand it is simply Amercan bought JG guns, reshimmed with metal bushings installed, so there works done for ya there with those.
I say look into the Classic Army, G&P and King Arms guns.