Hi guys,
I'm going into my second year of my PhD at Iowa. I don't have too much unique advice because I found my place from getting an email from people already in my program (Psychology), saying they were moving into a place and needed another roommate.
However, one housing company I would try to avoid (they do own a ton of places here) is Apartments Downtown. I haven't heard good things, and they were just found liable for having illegal leases.
http://www.dailyiowanmedia.com/live/2015/07/08/district-judge-rules-against-apartments-downtown/
I live on the North Side, which is a quieter area with fewer undergrads, and more grad students and families, which has been nice.