As pointed out above, it all depends on your valuation of the points. It appears that the MR points come out slightly better.
For me, it would depend upon how usable the points are. Since I live in a United hub city, MR points are not as valuable since UA is no longer a direct transfer partner with MR. I do use my Starwood points for redemptions and I have been able to get better than the stated minimums therefore, the Starwood would be my pick.