Thinking long-term, I believe that Bradley has more upside than Moore, so the Celtics need to commit to giving him enough minutes so that he has a chance to learn how to shoot in the NBA, even if costs the team a few regular season wins. I think sending Bradley to the D-League is probably near useless for that purpose.
With Rondo seemingly out for the next month, hopefully someone steps up and separates himself from the others while there are minutes for all three of them. I'd keep starting Bradley while Rondo is out, but keep in mind that just because you start, that doesn't mean you have to end up with the most minutes at the position.