By all accounts, I'm a newbie landlord. That being said, however, I appreciated using Zillow's background check service. (It also works through Trulia and something else.) For the prospective renter, their application and background check is good for 30 days for anyone they want to send it to through the app/site that can see it. Everything is free on the landlord side of it, and the prospective renter knows their money is going straight to costs and not some surcharge.
It may have been dumb luck for me on my first try, but it seemed worthwhile (job verification/history, credit check, criminal check, housing history, and other stuff). I'll let the more experienced landlords chime in from here on, but there's my $.02.