I'll be interested in hearing what Buyers and Sellers think of the two sites.
As an agent, I use both Trulia and Zillow. Both sites provide me with good exposure for my listings. There's a lot to like about them both. However, I also would like to see both Trulia and Zillow be even better.
Specifically, Trulia and Zillow have certain features that mislead and confuse Buyers.
It seems that every week (sometimes several times a week), one or more Buyers on this Trulia Q&A Forum want to know why a particular property is priced so low.
Just yesterday, we had a Buyer on this Forum who found at least a dozen properties "listed" here that he wanted to buy for cash because the prices were so outrageously low.
Agents usually know without even checking that the "listing" is really an ad for the Realty Trac lien tracking service. Nobody likes bursting someone's balloon, but then, as agents we feel compelled to tell the Buyer that the "price" is not really a list price--In fact the property most likely is not even for sale.
Zillow is misleading in a different way. Many agents and Sellers have observed that the value estimates on that site are sometimes wildly inaccurate. And I think I know one of the reasons it happens.
It looks as though Zillow is drawing an invisible circle, of a certain radius, around the subject property, and then comparing the property to others within that circle.
Of course, the problem with that type of (simplistic) comparison is that it ignores such things as existing natural and man-made boundaries (for example, major highways, waterways, or railroad tracks), subdivision boundaries, and (most important of all) neighborhoods.
It's hard sometimes for agents to take the Zillow valuations seriously when they appear to ignore some of the most important principles an appraiser would be expected to follow. Meanwhile, Buyers see these (often inaccurate) value estimates, and want use them to justify lowball offers.
There IS a way to avoid these issues, and that is to work with a Realtor who knows your local market. There are plenty of us here, just waiting to help.