Well, let's see if either of them are playing for anyone first.
If both play, and we're able to do a fair comparison, probably Peterson, as has been the case most years the two have been in the league. Peterson is a monster.
Both might actually benefit from the time off if they get to come back, Peterson especially. John Riggins took a year off in 1980 due to contract disputes, and he was able to play through '85, and potentially a large reason for that was due to his taking time off. The body takes a lot of punishment being a running back, and a full year off (while staying in shape) could potentially keep the wear and tear from reaching critical levels.
For Peterson, who will be 30, and somewhat for Ray Rice, who will be 28, the time off might extend their shelf life beyond the usual 2,000 carry mark (Peterson, of course, already being there).