I Swear by my VFC "Quake" M4, got it brand new for $530... Had it almost for a year shot the shit out of it over 15k worth of bb's... NOT a single misfire or jam. Although for the price now come to think of it id probably settle with a King Arms and mod the daylights out of it or pay a little more and go with a G&P. Like others said VFC is proprietry so not very customizable when it comes to internals over all very happy with the VFC
Go with a King Arms as others mentioned!
goodluck mate