Here is what I know:
1. The O-line prefers to block for one type of RB. They get used to a style and/or the timing of a RB. Tomlin has stated this as being the case.
2. Redman looked like he wanted it... he was not going to be stopped.
2-a. Too much spinning.
3. Dwyer looks like he has that burst, but can also knock someone over.
3-a. He gets winded too easily.
I see this as a "AB verus Sanders as rookies" type of situation: the player who practices better, gets the start.
What a nice problem to have.