Since you’re starting a Pittsburgh RB, Diontae is the SAFER play.
This is because the fantasy scores of teammates tend to be negatively correlated–if one is having a bad week, the other is more likely to be having a good week, and vice versa.
So the combined scores of teammates tends to be more consistent than the combined scores of similar players from different teams, so you’re less likely to get a low score from both of them at the same time. But the flip side of course is that you’re also less likely to get a big score from both of them at the same time. You sacrifice highs to eliminate lows.