I'd drop both, and pick up Stewart and McKinnon. McKinnon, even though he might lose goal line carries to Asiata, is a solid RB2 on a good team that will probably win a lot. And Stewart should be back next week.
Sims is kind of injured, and even if he's not, he loses his drop when Martin gets back next week or after the bye. Murray is definitely a lost cause in a RBBC and he's going to be hurt for multiple weeks.
If you had to keep one, I'd keep Sims just because he might have some PPR value even when Martin comes back, but I still like Stewart and McKinnon better.