The Troy-Bilt Z and the Cub Z are basically the same unit with different paint and decals, both made by MTD.
The JD rider is not a real JD, probably made by AYP or MTD. A real JD will say "Made in Moline" and hold its value.
Probably the weakest point in all of the three you mentioned is the hydro trannies. They don't have a filter or drain plug, and you can't change the oil.
If your friend is a careful driver and takes good care of his truck, don't gun it out of the blocks, is a stickler for doing the maintenance on all his stuff, that tells you something. If he ain't, that tells you something too.
If you just have to have a rider you can't afford commercial. A Lazer for 3K is pretty hard to find, I never seen one.
You have to weigh everything, make your business decision, and hope for the best.
I went with the wb, new, belt drive, eXmark Metro 32. Very reliable. Got a heck of a deal on it -- I think because everyone wants a rider and it had been on the floor quite awhile. It was right for me, but not for everybody.
FTC Takes on Music Teachers. What's next, peripatetic philosphy teachers and physical trainers?