Voted for Farscape.
I'm planning to watch the first season of SGU again soon after a couple of years. Would be nice to have someone else to discuss it with.
But in general I think you should watch something you never seen before, so you should watch Farscape.
For the record, they're doing a rewatch/first time watch feature of Farscape over at The AV Club at the moment http://www.avclub.com/tvclub/tvshow/farscape,419/