I'll play devil's advocate here, but as I've had both I can speak from experience. The ZT is a better handling car than a ZS.....before you all laugh at me let me explain. The ZT 190 on the original (harder) set-up is more adjustable and perfectly balanced front-to-rear so it can be steered on the throttle. The ZS is no where near as balanced and seems more prone to understeer thats not as easily balanced by coming off the throttle and getting the rear to play.
BUT the ZS is quicker because its lighter and has a better power to weight.