Unless one brand of KZ is way better than all of the others, then its always going to be a question of which KZ is best for the track you are at. Better off with Stock Moto.
I don’t think the KZ class (TRUE KZ engines, I should point out) suffers from the same nightmare that is currently plaguing the TaG class. Namely, trying to equalize all of the different TaGs brands together under one race group.
Despite it’s disadvantages, the KZ class has a big plus (compared to TaG) in that it’s a homologated class, strictly regulated by the CIK. All KZs use ONE ignition, ONE size carb, the dimensions of each pipe is homologated, the CC volume is regulated, and the exhaust port opening is controlled.
TaG isn’t like that. The engines are all vastly different, with different carbs, ignitions, RPM ranges, pipes, etc. that creates the “this engine for this track, that engine for that track” mess the class suffers from.
Also, I’m not sure how CIK homologation works now, but I don’t think any KZ manufacturer can produce a major re-design of their motor on a whim right before a major event; theoretically, an engine brand could make a sudden change at any time in TaG, which further muddles things.
Are some KZ engines better than others? Yes. Does a specific model of KZ improve with each homologation? Yes. Can an engine builder significantly improve on a KZ in stock form? We all know the answer to that one. But I think the nature of the rules and regs that KZ runs under prevents the sort of “certain model for a certain track problem” that TaG suffers from.