Inefficient outside shooting and lack of skill guarding the perimeter in this era limits Henson and Chriss to undersized Centers/Bigs. The Kanter signing completes our Center/Bigs rotation.
Millsap is a Center/Big as well (he was guarding Kanter in the playoffs), but he is efficient enough at the above qualities that teams will still play him at the 4. With Batum, Rudy Gay, PJ Tucker, and Jeff Green off the board itís slim pickings in free agency. Millsap might be the best option, Justise Winslow is a last resort.
That said, my preference is to trade draft compensation for Joe Ingles, Kyle Anderson, or Larry Nance (in that order).