Sullinger and Olynyk are PF's, neither are centers. Neither of them should be defending the center position. Sully comes closest to being able to defend the 5, but he is certainly not the ideal guy for it.
Fav and Fab *are* centers, but Fab isn't ready and we don't know if Fav is good enough or not. One or both may start at C, but not early in the season.
Wilcox won't be on the squad. Shav was waived, Wilcox was never re-signed.
So, if these are the C's only options, I think Humphries starts. He probably keeps starting until someone beats him out or he is traded.