Many school's websites have class profile information that shows the acceptance rates, GPA, and other stats. I applied for the 2010 MSW season and at that time there were huge amounts of people going back to school and the acceptance rate was a lot lower than it is now. In you personal statement show that you know what you are getting yourself into, that you have overcome adversity, you understand policy, and that you will be a great addition to our community. I would go to a highly ranked MSW program that will best holistically meet your needs so that you can get what you need and have a leg up by the name.
The ivies aren't really known for their social justice programs: http://grad-schools.usnews.rankingsandreviews.com/best-graduate-schools/top-health-schools/social-work-rankings