I generally watch sub.
For Z, all English versions base off the same scripts (except DBK, which is more accurately dubbed).
For DB, I think the Blue Water dub is from French. I only really watched in Japanese.
For GT, the Blue Water dub is the superior one, based (I think) directly on the studio translations, and adapted faithfully, unlike Funimation's major rewrite. (DBK was dubbed by Okratron, not by Funimation proper.)