ICS sportlines. Of all the cheap piece of sh*t guns around, these,the JG G36C and CYMA CM045 are my top picks.
G&G Wombat Musheens are nice and all but ICS has a far better & more long term reliable gearbox,the shell's stronger,it has steel bushings,gears are better,and the split design is easy to maintain and more durable.
However the hop up unit isn't as good as G&G,the bucking is usable though. With about 9 minutes of filing you can get a Tokyo Marui type hop up in there easily.