I'd say "Ulysses," because it was published first, and "Journey" works as kind of an answer to Joyce's paean to the common man (Celine's response: nope, we're all terrible).

That said, for my year I finally read both "Ulysses" and "Journey to the End of the Night." They function surprisingly well as literary companion pieces, each the other's Jungian double.

I'm not sure why "Ulysses" counts as a study of heavy drinkers. There's surprisingly little alcohol consumption on the page; maybe I'm misremembering, but doesn't Bloom stop after a glass of Bordeaux with lunch? Dedalus and the med students get ripped out of their heads but that happens elsewhere.