This is a great question. When it comes to Fantasy, I always just 'do'. The more you sit and think about something, the more it festers, and the more likely you are to make a bad decision. With this mindset I have won a significant amount of leagues and $$. BUT... that being said, know this - I never hesitate. I was fortunate enough in one of my Dynasty leagues to acquire both of these players, and I don't even know where to begin on this one. When MJD starts warming up around week 6 or 7 (which is when I think he might), I'll rack my brain to utter insanity every week. The best I can answer is this:
Contract holdouts never end up good. I mean, really, like rarely ever. Had you of asked this last season around game 10 or 11, I would have told you to flip a coin. But MJD has missed time, reps, ect. ect. ect... For game 1, I would go with Sproles. Sean Payton not being there could make him melt faces, or just give a semi-solid RB performance. With MJD, the uncertainty just doesn't sit well. These are just my opinions but I hope they helped you.