Worst: G&G MP5A4 simply because I haven't skirmished it since upgrades. Originally, it felt like the gun had lethargy and would barely cycle on semi. Full auto was hilarious. It was like I could hear the spring compress and struggle to get that last bit of compression before the gears would cylce enough and let the gun fire. Post upgrade testing; this thing is nuts. Turned it into a high speed build and holy shit, on a 11.1v LiPo it's fast af. Just wish they made aftermarket MP5 triggers.
This worst gun could very quickly change as I think i'm close to securing a deal on (what I think is) a G&G CM18 Mod 1. The idea is to fix up some small issues with it, give it a bit of TLC and see if my brother wants to airsoft. If not, turn it into a little project gun, see what I can do myself.
Best: Krytac LVOA-C. Aesthetically it's fantastic. Changed the stock to a Magpul CTR one, changed to a Prometheus 6.03 barrel. Only real negative about this gun is the hop unit, specifically the hop arm. Attempting to use anything other than the original Krytac nub/tensioner was pointless. I eventually gave in and bought a Laylax/Prometheus metal hop unit which has a much better hop arm that can accept aftermarket nubs without issue. Gearbox might be noisy but it's always performed well and, so far, just keeps on working.