If you are thinking about transfering through Hilton, add an intermediate step by transferring to an airline (say DL, for example) first, then transfer those DL miles to Hilton. A direct transfer from MR to HHonors yields 1,300 HHonors points per 1,000 MR points, but 1,000 MR points yields 1,000 DL miles which in turn provide 2,000 HHonors points.

Of course, the problem with laundering via HHonors is that you will take a tremendous haircut when you convert HHonors points to AA miles (i.e. 10,000 HHonors points only yield 2,000 AA points).