IDK, this one can go either way.
I stayed away from Westy and Addai in all leagues and will attempt to continue that trend.
I think McCoy and Brown are both just too good to not earn touches even if the other two players are healthy. McCoy might just keep Westbrook healthy though, he is good enough to create a committee in my humble opinion.
Addai sucks in my humble opinion and eventually, this season, he will take over the #1 role, but if both are healthy, again, I think you're looking at a committee.
Addai hasn't exactly been the model of health either, remember that.
I honestly think Westbrook misses a maximum, standard Westbrook issue 1 or 2 games, so I think I stick with Brown, who may earn up to a whopping 12 starts by seasons end due to a combination of Addai's suckitude, frailty and Browns skills.
Sorry I've been answering in riddles

but these two guys are literally my most targeted, late round backup RB's in all my drafts so far, so I don't know how to answer but how I have.