I've had every airsoft MP7 in existence at one point or another - get the TM GBBR, the 1:1 Scale ones are a completely waste of money.
WE: Magazine gas efficiency is by far the worst of any SMG, Hop unit is a joke, 10 inch grouping at 20ft. the trigger needs to be rebuilt OOTB to last longer than a few game days, very vague fire selector. Gen 1 is horrendous, Gen 2 is only marginally less crap, but at least the trigger lasts longer than a few game days. New Wave is just a gen 1 with a slightly better trigger group.
VFC: Well its VFC for a start, so don't expect anything to last long. Mags leak like buggery, it came to me doing 420fps with no immediate availability of any velocity reducer (got it at launch), Mag efficiency was pathetic.
KWA/KSC: NS2 system is brilliant for gas efficiency, unfortunately the gas reservoir is smaller than most and as such efficiency is only OK, NPAS or equivalent is a complete PITA but necessary as it can come stock as high as 460FPS.
TM: Will need the stock nozzle replaced at some point if you're using Green Gas as propellant, so order it before it fails Other than that, by far the best of the bunch, reasonable mag gas efficiency, reasonable FPS (mine was doing no higher than 350 on green gas with the hottest day it was used on being 31 degrees C), Decent, reliable hop.