Hey otforeva. I think it depends highly on the population you are hoping to work with. For example, I am set on working with Veterans and Active Duty Service Members in Mental Health, I will have a large focus on invisible injuries like Post-Traumatic Stress and Traumatic Brain Injury. For me, there are schools that the OT dept provides the on campus student support services for Student Veterans so that is how I figured out the schools I thought were the best for my "Military mental health" focus. Are you hoping for general practice in MH where you serve all ages? Or is there a specialty you are looking into?
In addition, a great thing to do is research the professors that are on faculty at the Universities you have interest in. This is how I found some great schools for OT in serving the Military population. Most OT Departments have faculty pages that shares their background and practice experience, as well as their research focus if they have one.