VFC is relatively new to the GBB game, entering only a few years ago. But true to their AEGs, their externals are spot on, great quality and feel. I haven't had hands on experience with any of VFCs GBBSMGs or GBBRs, only their pistols, such as the M&P 9/c and PPQ.
My most recent experience with a WE open bolt M4, I wasn't all too impressed with it. But as the system has been around for a while, the is plenty of aftermarket support for them.
I would probably go with the VFC.
Though, hopefully someone else with more hands on experience will drop some input.