the ics one isn't bad, it's slightly upgraded over the tm as a clone of the design. The only drawback is the way the hop is adjusted, the lever is not very tight and has a tendency to move around. You may need to find the adjuster upgrade. I think prometheus makes it. The parts make the adjuster a lot tighter so it hopefully stays put. The only other issue I have with ics mp5s if you are looking at the A models and not the SD models is the cocking tube and front end might have a bit of wobble to it, but you can minimize it with some bracing.
The g&g you have to deal with the bs toptech blowback system which I am not a fan of. Their gearboxes of made of cheese so they will crack no matter what you do. Their hopup system is a bit better in that it's a slider more like an ak unit inside the ejection port.
classic army also has their own hopup unit design also inside the ejection port, it's also a slider. But CA is notoriously weird with their manufacturing specs so aftermarket parts might fit poorly.
vfc makes a mechanically operated burst firing mp5, it has some proprietary parts to that mechanism which can probably be found and replaced direct from vfc. Not sure how their hop works, I would assume it's internal to the ejection port.
src had a beautiful stamped and welded steel upper like the real ones, but they are hard to find and src's manufacturing tolerances are weird. It's also got an ejection port accessed hop with a slider.
cyma is a clone of the CA I think, but their exteriors are heavy, however they have been known to be pretty decent guns. I've known a few people that have had them and had no complaints aside from weight. They take upgrades well.
JG/E1 are also pretty good, I think they also have ejection port accessed slider hopup units, but they're hard to find these days.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.