Sorry when I was talking warranty, I was talking commercial. I have no idea what residential warranties are on any of them.
The deck adjustments are somewhat helpful. Set decks (without adjustments) usually will either cut southern wide stem grass well or northern fescue well. But will not do both well. Some decks have the ability to handle tall field grass (6"-12") much better than others but then usually will be a weaker deck in manicured turf. The adjustments are an attempt to make the deck fit more of these different scenarios. Different mower blades can also help and hinder this.
Exmark is a quality mower. IMO they have done little to improve a good product in the last 12 yrs. I actually like their older model mowers better than the new out now. I know the first year or two of the new style were rough with quite a few problems but I'm sure they've worked them out for the most part by now.
Speaking from experience. Don't let the hustler hoses bother you. I've logged 1k hrs. on more than one with out any problems. They use to state a lifetime warranty on lines and fittings. I'm not sure if that's the case any longer. I actually like the separate hydro pump/wheel motor set up better. It's probably the automotive tech and farm boy in me. But I feel that the heat dissipation that occurs going from one unit to another alone is a plus. I honestly think it's the best hydro system of any brand out there bar none. Also Hustler SZ have the full front leading edge baffle that is adjustable.
I don't believe Gravely has any available adjustable baffles.
These are all good machines. The QOC would be my biggest concern and the only way to tell if it will cut the grass well in your are, is to well.... cut the grass. Demo them an hr each in worst case situations. Thick, wet, weeds, tall, etc.