cyma: 028 are great starter guns, anything from 030 are good guns as well, the newer 040's onwards are crackingly good guns for the price.
JG: Not bad, just not as good as cyma for ak's
Cybergun, I think are rebadged dohboys, again nothing wrong with them for the price, though dohboys can be slightly tempermental with magazines, but shaving 1mm off the mag catch sorts that out.
The only thing I would say is that they are normally a bit hot for UK sites, so may need a spring downgrade. Most cyma are 360-380fps and dohboys can be anything upto 420fps! They are worth checking forst before spending the money to get them downgraded though.
have a look here and read some reviews on cyma, dohboys and jg guns
http://www.airsoftgi.com/product_info.php?...roducts_id=3310
I read a lot on that site, taking the average review and based my first purchase off of that.