Who do I start, M. Brown or M. Williams?! (1 Viewer)

Do I start M. Brown (If Gurley sits), or M. Williams in flex #2?!

12 team .5 ppr start 1 QB, 2 RB's, 2 WR's, 1 TE, 2 flex (RB/WR/TE), 1 Def I am 0-5 need help! 

QB: D. Watson 

RB's: A. Jones,  P. Lindsay,D. Montgomery,, A. Mattison, M. Brown

WR's: O. Beckham Jr., R. Woods, A. Robinson,  Juju, M. Williams

TE: G. Everett, H. Henry 

Def: Vikings

Thank you

Brown for sure if/when Gurley is out. If Gurley isn't out, I might sneak Henry in there over Williams, assuming he's playing.