I like a company that makes a good gun out of the box; however, upgradability is inevitably the end game. I'd pick a manufacturer that stays true to the old Tokyo Marui designs. Good tolerances and easy to work with; that's what will make the difference. G&G, CA, KA will all upgrade well, and are simple to make into a reliable and tough AEG. To be honest, I haven't had much to do with KWA other than their pistols.
On to your question. Get yourself a .22 cleaning rod from Canadian Tire. It has everything you need to properl clean your barrel. Do not use the gun oil that comes with it; in fact, throw it out. Also put a single ring of electrical tape around the joints of the rod; you don't want to scratch your inner barrel. When swabbing your barrel, never force the cloth through your hop-up, lest you want to tear the rubber. Soak your hop-up rubber and bucking in Silicone oil, then dab it dry with paper towel. A good aggresive bucking will help with BB flight; which goes hand in hand with checking your airseal. If your BBs go wild, then either your bucking is not seated right, there is debris in your barrel (like oil), or your BB weight is too low for your FPS. Running 0.25 BB bastards for your speed, and all around BB isn't a bad idea for an AEG. If your gun shoots 380 FPS with a 0.20g BB or faster, you may want to look into a 0.28g round for stability; you will lose travel speed though.
ďREALITY IS LIKE A STONE. TO MANY ITíS HARD AND COLD, THEY CANíT HUG IT OR EAT IT, IT ONLY FRUSTERATES THEM AND DOESNíT DO THEM MUCH GOOD. TO OTHERS ITíS STRONG AND DEPENDABLE, YOU CAN BUILD WITH IT, BUILD UPON IT, OR WORK WITH IT, ALSO USE IT TO SMASH PEOPLE IN THE FACE.Ē