I've had the KK reg and 2x micromatic regs plus an inline one (because I sold a keg system when we moved interstate and bought again, not 2x because it broke).
The KK shat itself and I lost a gas bottle.
Micromatic - buy once, cry once.
The current model uses a small hex key for adjusting and it's brilliant. The inline plastic one is great for either gassing one keg high pressure and one at serving pressure, or one at British carbonation, one at higher carbonation.
I have no experience with Harris, I've only heard good things but from what I have researched, it's as good or marginally better but a lot more expensive.