Hi there, and welcome to the Cafe! Great to see a new face around here and I hope we're able to help you out and you stick around in the future
Caddy has a bit more upside and a similar floor given both backs' situations this week, so I think I would start him, but Tolbert is enticing for his own reasons. I just really like what I saw from Williams and don't see Jackson playing or, worst case, doing much if he does play on Monday night. The G-Men are decimated on defense and the Rams actually looked pretty good last week with the Caddy out of the garage, so I think I'd have a hard time starting an - albeit part time - "featured" back for Tolbert.
Hope this helps!