I won one or two challenges back in their first forum incarnation. I couldn't remember which themes, but just looked them up in the challenge compendium thread NOBD & Spoo put together then, and it seems like one was the Black theme and the other was the FU jacket one. I can't remember the details of what I wore for them though. My first theme selection was Pattern Frenzy (compile a fit with as many patterns as possible, but which still actually looks good and not like a dog's dinner), and the second was Inspired by Nature (fits to be inspired by something - colours, patterns, textures, whatever - in the natural world i.e. trying to get people to think about how to craft a look by having an end image/muse in mind, rather than just throwing items together). Both themes had potential for high achievement, and terrible car crash failures and IIRC I think they generated both.
I think that's important in a challenge: at their best, they provide artificial constraints that result in creative/unexpected solutions to the problem of looking good. I like seeing what problems the constraints generate; it's another way of figuring out what you actually like to see in the mirror. And at their worst, a tough challenge theme means that you can giggle at the terrible submissions. I don't know what theme I'd pick if I ever got the opportunity to pick again. But I'd probably pick similarly high-wire, high risk/reward types of theme.
BTW, I forgot to comment earlier on RDiaz's jacket and his feeling of discontent about its silhouette. Personally, I would agree with those thinking it looks very nice in general, but would benefit from a somewhat less cutaway front. Apart from that, I like the rest of its appearance. Of course, the more important thing is whether he likes it. If not, before ordering another jacket, it would be worth figuring out what he'd ideally like from a jacket that this one isn't giving him rather than over-focusing on individual construction elements i.e. take a holistic look for an archetype of the kind of jacket he wants and then finding out whether his tailor likes making that sort of jacket.