Should I pickup Sanchez or Manziel?

I have Rivers and Tannehill. No ppr, QB basically gets points off yards and TDs. I've got Lacy, Murray and Jennings as my backs, but afraid I might not get the production out of them this week. Was leaning toward going with picking up Sanchez or Manziel to play at QB instead of Rivers. This is playoff game to see who goes to championship.