A grand cherokee and cherokee are different.. Just wanted to get that out of the way..
I would like to know more about the both of them.. millage, body condition.. But just on what you said.. the 4cyl auto is a total dog. you will hate it I think especially with the the larger tires. The ZJ will be more useful then the YJ.. lots of space and can tow if you want it to.. 5.2 or 5.9 V8? The biggest downfall might be that it has the full time NP249 transfer case.. but it's tollerable.. With the YJ you'll get the option of doorless and topless when the weather is nice and the NP231 transfercase..
If it's me and im picking between those two, I go ZJ
Edit: The overall stock drivetrain and parts used to build the ZJ were stronger then the YJ for the most part as it is a heavier duty Jeep.