unlike paintball, there's no real prizemoney in airsoft, there's a few tournament games I've seen but there's not really any prizes involved. The sport is still sort of growing, whereas paintball is very commercialized and big business.
As for guns, just about every manufacturer makes an m4 and like Drake said, some are better than others. But some have seen awesome results form shitty/cheap guns with some tweaking, vs some seeing shit results from a nice gun... but the odds favor nicer guns performing better.
The reality is that all airsoft guns will suffer mechanical failure eventually, so what you're really only buying is the quality of the frame (gun externals) around the gearbox, since everything in the gearbox (including the gearbox itself) is replaceable.
To ensure the ability to do this you should be shopping for a gun that's tokyo marui compatible since the majority of the parts are made for tokyo marui designed guns. Since they are the grandfather company of the AEG most manufacturers used them as a template.
Only when you get into more unique gun platforms will you see some more uniquely mechanically designed guns or the few manufacturers that went their own way.