I can't use a GS because they can't handle the type turf I mow much of the time, but there is something to be said for the way you stand ON the unit rather than trailering or walking behind it. I find that as I get older I notice it more, but it does take noticeably more energy (and wear and tear on ankles, etc) to use a sulky/wb than to just stand on a platform. Probably because you are not fixed in position behind the machine, but also because a sulky just has limitations in its shock absorbing capability vs a spring loaded platform. But even then it's less taxing to just sit. So I use ZTRs whenever possible. What would make much more sense to me would be a ZTR that coverts to a wb, like the one currently sold by a small company, except done by one of the majors that is fully featured (true mulch system, lower center of gravity, better baggers available, etc) and has a more established reputation for cut quality, durability, etc. I suppose if you only needed the walk behind capability occasionally, you might try a GS (as it can work as a wb in a pinch) but if you really need wb's for their advantages on hills, delicate turf, etc, I'd stick with the tried and true TT.