for me, it's definitely Closer.
with Unknown Pleasures, the production is both a strength and a weakness. the polished, icy sound gives it such a cold feel somewhat like numbness, which works incredibly well on songs such as Disorder (my favorite from the album) and New Dawn Fades, but takes away the edge that i love so much in JD's live material. i have very mixed feelings about it, but Closer is masterfully produced by Mr. Hannett.
so in a sense, UP is over-produced, but it doesn't qualify for me as an absolutely over-produced album. but Technique and Republic do (sorry, Technique fans). the thing that keeps me from loving Technique as much as Low-Life is the incredibly polished sound; i just can't get as into it. the piano hooks and guitar lines are just too clean and pretty. i mean, i still love the album and think it's amazing, but i just can't enjoy it as much as Low-Life or even some parts of Power, Corruption & Lies.