I am having a hard time deciding what the top priority is, Guard, Wing, or Big. In my mind, this is what we have now:
Guards: White, Holiday, Pritchard, Mykhailiuk, Springer
Wings: Tatum, Brown, Hauser, Brissett, Walsh
Bigs: Porzingis, Horford, Tillman, Kornet, (Queta)
If we are going to continue to mostly play with 1 big and an extra guard or wing, then another guard or wing (Oladipo?) is probably more useful than another big (or an upgrade to Queta). If we are going to go back to playing more 2-big, then I think more of a PF type who can shoot (Gallinari or Bertans or someone like that?) would be a more useful add.
I personally would lean more towards adding more of a PF and playing bigger more. Or just doing nothing and converting Queta to be on the roster for the playoffs.
We have some flexibility in that Brissett for example can be in the wing group or the big group. Mykhailiuk could be a guard or a wing. So if there is someone better we need to fit in, others can shift to balance things back out. And I feel that Mykhailiuk could still be waived/bought out, if they pick up someone better and decide to convert Queta.