I find it hard to decide as everything* they did from 1980 to 1988 is sterling. I think Kaleidoscope, Juju, A Kiss in the Dreamhouse, Hyaena, Tinderbox and Peepshow are all in the same league as each other. But I think their crowning moment is either Tinderbox or Peepshow, but Tinderbox wins narrowly because of Cities in Dust.
*everything apart from Through the Looking Glass which I haven't listened to and don't think really counts as it's a cover album. That said would anyone who's listened to it recommend it?