Your best bet for referrals is getting someone you know who uses a property manager to tell you about their experience with property management.
Another approach is to look around at specialty firms and see which ones have been in business for a number of years. You can't stay in a business for a long time without some degree of quality.
Check the history of the property/company, the BBB, and other sources. Most of them are usually reliable, they use different methods to qualify the tenants for everyone's protection. The law tends to favor the tenant these days.
However, any large rental property and most property managers are members of the Apartment Association, and therefor usually have to maintain good standing (no too many complaints, etc.).