ZT's are generally much quicker once you become accustomed to the controls, especially if there are lots of obstacles like trees & garden beds to mow around & reach further under shrubs/overhanging plants.
Tractor type mowers are in some ways easier/more intuitive to operate & are more stable in operation on steeper terrain - they'll also be happier hauling a trailer & will pull other implements or push a blade (none of which a ZT is really designed to do...)
The ride/handling of each is a little different, as is maintenance (e.g. ZT have the motor behind the cut which generally means more cleaning of air fiters & if fitted radiator screens etc..), deck removal, storage....etc.. ..these all come down to personal preference.
As to which ones better ? Neither really, it's "horses for course" - I'd have a ZT every time in the right conditions & if all I wanted to do is mow, but I now only run tractor types because of added versatility/undulating terrain.....