Well in this case they are virtually the same thing..... Externally all P90s are virtually the same. They might use different material but overall they are all still the same thing. Same with the internals. G&G has good internals as does King Arms.
It all comes down to personally preference. I personally prefer King Arms over G&G because I think their internals are more superior however I know for a fact the G&G as of late has started to make a lot better guns internal wise, so again it is a toss up.
My philosophy is that if you don't change anything internal wise (gearbox) your gun should perform without a hinge. However you run into problems when you start to take it apart, a lot of times people don't know how to put their stuff perfectly back together and end up with faults in their guns.
I suggest the King Arms cause it has been out for a while and is reliable, however the G&G just got released so I cannot easily dismiss their P90 until it has been tested as much as the King Arms has.
In the end it does come down to the features, if you still can't decide flip a coin.
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