Of the two, I'd rather Faried. He can really rebound and help us with hustle and energy scoring inside, on lobs, pnr, etc.
His main drawback is that he is signed for another 3 years at 12m per year.
http://www.spotrac.com/nba/denver-nuggets/kenneth-faried-8073/But he would certainly help us with our rebounding issues.
Nurkic just seems to be a more experienced but less talented Zizic, so that move probably doesn't make sense for us.
It all depends on the price. If we are swapping Amir Johnson or Zeller and a 2nd or low 1st for Faried, I'd probably do it.
But we do decrease our trade options for matching salary in the future.