Thats pretty tough...I think this is one of those rare cases where you go by your own gut. Honestly you cant really go wrong. Maybe Rice has an edge over Slaton but Buffalo is getting torched on the ground this season. MJD is for sure though.
I WISH I had your problem. I'd go with MJD and Rice. While Slaton has the better matchup, Rice tore up the MN D which is as good if not better than the Denver D. I'd feel safe starting Rice in pretty much any situation.
MJD is an obvious pick, but Slaton v Rice is more difficult. I would have to go with Slaton on this one, he's playing a squishy Bill's Run D while Rice will be perused by a pretty consistent Denver D.