@Austin Rose, instead of zillow, you may want to look at www.loopnet.com for duplex, triplex and fourplex listings. You may find more properties to compare.
As for the SFR vs Duplex argument, there are many things to consider. A couple of those are; are you single or married with kiddos? What is YOUR investment goal. If cash flow is your primary focus, why not look into a triplex or fourplex which will all qualify for the same loan options as the duplex or SFR, all else being equal. You can still live in one unit and rent out the other 2-3 units for positive cash flow.
However, if you'd prefer to sell the property down the road for a good chunk of cash from appreciation, a SFR is going to typically appreciate much better than a multifamily unit.
How do you feel about being a property manager? If you live in the multifamily property, management is almost inherent. Granted, you could still pay someone to do it. But since you're in the property day after day, paying someone else to manage it makes less since. However, if you buy a SFR and you're not very close to the property all the time, you might consider professional property management. While that may give you peace of mind and less direct tenant interaction, it'll also have to be factored into your cash flow analysis.
I'm going to stop here for now. Hopefully this has given you some good food for thought.