Honestly, I don't think there is a great way to determine which programs are great. If you use USNews report's ranking, you'll see that the methodology they use is very...qualitative. Furthermore its an evaluation of the CNS program from 2011 data if I recall.
Furthermore, I think that all of my clinical education will be self-directed. Every program will teach you basic health assessment, patho, pharm, "research", etc. But to actually learn how to do proper psychiatric interviews, psychotherapy, psychopharm care etc - you need clinical hours. According to Gladwell, probably close to 10,000 hrs. I would go to a school that has plenty of opportunities for extra-clinical training opportunities. Thats just me.
At this point, what I am then most concerned with is - how will where I go to school effect my post-graduate opportunities. The people who hire PMHNPs are usually physicians. Even at my current large research hospital, the psychiatry department tells the hospital's NP Human Resources Dept of their need, and then the Psychiatric Medical Director interviews and hires candidates. Every PMHNP he has hired has gone to a traditional brick and mortar school, they were MSN prepared, and had good experience.
When I had a chance to pick the brain of this physician, he highly discouraged any "online" programs. Know your audience. Don't listen to these people on the internet espousing how great the University of Walden or Phoenix University is. I don't care whether they sponsor this website or not. How will the people who will hire your evaluate your graduate education? If you see a candidate from NYU or JHU vs an online school, you can bet the former will be more highly regarded.