How are these tractors comparable regarding serviceability? Are bushings, bearings, spindles etc. greaseable, sealed diff housings vs serviceable, etc. (If this even applies here). Hydro pump size/filtration capabilities - bigger is better. Stamped deck vs fabricated deck - fabricated decks are almost always built heavier and last longer than your typical thin gauge stamped deck.
Servicable vs non servicable parts...more or less the difference between greasing parts and changing parts... eventually they all wear out but as you well know being able to grease a component generally increases the lifespan.
I know in the zero turn industry many of the manufacturers use the same core parts - engines, hydros, etc. It really comes down to how well the machine is built, quality of components used, and findin a package your comfortable with.