Hi HannahJoy and Zayah,
That's actually not the whole story in regards to Ann Arbor. While it's true that Ann Arbor city proper is affluent and not very socioeconomically diverse, it borders Ypsilanti to the east, which is an incredible racially and socioeconomically diverse area. 30% of the residents in Ypsilanti live in poverty; 40% of those 18 and younger. The median family income is just shy of $36k. Ann Arbor is also only a 30 min drive east to Detroit, and just about everything off I-94 between Ypsilanti and Detroit is racially and socioeconomically diverse. Ann Arbor is a pocket of wealth, but it's closer to the exception in that area. Also, while Ann Arbor is reasonably populated, the city itself really isn't that big in terms of actual area, so you should expect to travel outside of Ann Arbor city proper for field placements, likely to places like Ypsilanti.
How do I know all of this? I'm from Ypsilanti and I lived in Ann Arbor for 5 years before moving to Chicago a decade ago. I'm starting the AM program at UChicago SSA starting in the fall. Just for some perspective, for the UChicago field placements, I'm expected to be able to travel anywhere within the entire 228 square miles of Chicago city proper plus 44 surrounding suburbs. Ann Arbor, by comparison, is only 28 square miles. Considering the nature of the work we hope to do as social workers, it seems unlikely that your field placements would stay within that 28 square miles when the true southeastern MI diversity is outside of it.
All of this is to say, don't discount UofM if you're into their program.