IMO this is heavily dependent on what status you're planning to achieve with the secondary program and how much you'll stay with the program in future years.

For example, if I were aiming for a backup program for footprint, I'd go for MR Plat mostly because I value the 4pm checkout and it's pretty easy for me to make Plat with the potential 30 nights from CCs. But if you aren't planning on staying much at MR in the future or achieving Plat, I'd recommend just being a free agent and choosing the best properties, especially if you are going to be doing limited service on mileage runs. In that situation I don't think you're going to extract more value out of program loyalty than just picking the best property case-by-case.