I have both WB and ZTR's, my biggest complaint with WB is they can be dangerous with a velkie and I have several types of velkies. You have to make sure the safety stuff is right.
It all depends on what you are cutting but a combo of a 36 and 52 WB with a 72 inch ZTR has the potential depending on properties of being the most cost affective setup!
A 72 inch ZTR a good one is by far the best money maker mower I have ever used. A 72 Super Z HD will leave a couple guy's just sitting there with WB velkie combos on a large property. Just look at what Puppy cuts with his and how fast he gets it done.
ZTR's are pigs however and a WB cuts much nicer overall and I love them for versatility as well.