Depends. I would rank Southside last.
Coopers -- smoked over mesquite coals, has a unique, very Texan/cowboy flavor. As for how tender/moist it is, depends on how long they had it in the foil.
Kreuz's -- a solid choice. Will be pretty moist. Smoked over oak, very traditional. The "standard," if you will.
Black's -- there's argument over this one. I've always preferred Kreuz's to Blacks. Some feel the other way. Both are good, and are very similar.