From those guys, it is definitely Nurkic. While I (kind of) like Noel, his contract status is a problem. The C's couldn't really hold onto him past this year while also using the cap space to upgrade another position. And I just don't think he is good enough to warrant what he will most likely get paid.
Really though, the guy I want most is Okafor. He would cost more than Noel, but I think there is a lot more potential there, and the contract makes more sense.
Of Noel and Nurkic, you take the one that you'd either a) rather have on a long-term deal, or b) costs less if you're uncertain you'd like either for a long time. While Nurkic would preserve space for next season, acquiring a max deal next summer requires us to let Olynyk go (not an issue for some here, I freely admit), and presumably one of IT, Bradley and Smart the following season. Nurkic also hits free agency in 2018, so that would probably mean he is out the door too, or causes two of Bradley, IT, and Smart to go.
I guess what I'm saying is that a max deal this summer will cost us several players over the next two summers, and so paying extra for Nurkic just to preserve that cap room might not be as useful as it seems. If either Nurkic or Noel seems like a long-term solution, that's the one you go for, and eschew free agency this summer. Otherwise you just get the cheapest of the two, or go for a stopgap like Bogut.