Which hop up unit should i get?

i have a full metal agm 614/416, metal lower and upper reciever, i want to upgrade a lot of things, starting with the hop up, i will be getting a systema bucking, and a polarstar concave nub, i will also be getting a 6.01 or 6.03 tightbore, 550mm, and a silencer, but for the hop up i want a full metal 1 pice m4/m16 hop up, im stuck on either King Arms or G&P, i was leaning torward KA because even though its a little more than G&P, it is in stock on evike, and i want to get all the parts at the same time, if i went for G&P i'd have to get it on another website, but if G&P is better i wont mind, people also said although the KA clip really locks in the barrel, it can break easy, and isnt sold by itself, so which one guys? id love to know which one pairs up best with the systema bucking and polarstar nub