On the subject of tire marks, I'm inclined to believe that for a given deck width and horsepower, a ZTR will weigh more even before your add the weight of the operator. However, one assumes the tires are correspondingly larger and will compensate. However, I'm not at all certain this is the case.
As for other dimensions of an comparison between ZTRs and walks, I suspect the traditional trade-offs still apply: ZTRs are faster and handle wide-open spaces much better, walks handle the slope work much better and weigh a lot less; ZTRs won't wear you out as much, walks are cheaper and better on a buck's worth of gas.
Realistically, you have look at your route as it stands or as you anticipate it will look next year and base your decision on that. I have way too many lots that are small, sloped or both to make full use of a ZTR, so my eXmark TTHP52/19 is ideal. But I simply cannot comment on another person's route sight unseen. You have to ace that out yourself.