Spec’s lineup has always been HardRock, RockHopper, Stumpjumper, with the Stumpy at the top.
There’s always been a couple of different “trim levels” of each model, and they’ve used those nameplates for decades, so there’s literally hundreds of different bikes under those three names.

Generally, I’d say that a Hopper would be a better grade frame set than a HardRock of the same year, but you’d have to dig into the specific catalog for the year of the bike you’re looking at.

It may be like Cannondale, where there were only one or two grades of frame, shared among several different models; distinguished by the wheel/fork/component builds.