Offering the max to already established players is not good enough to build a contender - unless ofc the contender he is a top-20 player.
Of the players in the list, only Horford and Whiteside are in the top-20 cat, and even they are borderline cases. I would still have doubts about offering Horford the max, his career seems to have reached the point where it starts to decline; as for Hassan he is unreliable esp. since he will be trusted with a fat contract for the first time in his career.
Someone like Noah (or Pau for that matter) would be fun to have in a team that already is a contender: good value for money, veteran savviness and experience. But I don't see much point in adding a player like that to a young team: these players want to close well their career with a deep playoff run, they usually mix badly with players in their early-to-mid-twenties who are still learning how to survive in the league.
So we are left with Ezeli, Mahinmi, Mozgov, Biyombo. None of them is worth the max IMO but some of them will get it (Biyombo has good chances if keeps playing like he did in game 3 against the Cavs; Ezeli has a good reputation in the league too). From my perspective it all depends on the money and length of contract they will ask for; I would stay away from getting in an auction for mediocre (or at any rate, not 100% established) talent.
tl;dr Mahinmi or Mozgov
EDIT: strokethrough typos