I have the same question, as I have both Dwyer and Williams, but I personally feel that Williams is a better start over Dwyer and Vereen.
According to Rotoworld, Stewart didn't make the trip, so he won't be filling in, and I feel D Williams getting the whole game, with temporary spells from Tolbert, I think he can actually perform. Chiefs aren't that great against the run, although they don't really have much of a passing game to worry about.
Dwyer is sharing with Medenhall, who has the case of the fumbles. Still, I less of a fan with the timeshare and really think Dwyer. With Roethlisberger out, I think the Ravens can't step up against the D a little more.
Vereen isn't rosted in our league, and CBS says he'll have a tough matchup over the Dolphins. He's also the second option.
I'm leaning towards Williams in my game. As I said before, I'd also be interested in more opinions.