As a landlord I have referenced both Rentometer and Zilpy. Rentometer doesn't ask enough info about the apartment to give an accurate value. It only asks about the location and number of bedrooms. It seems to have a fairly accurate source for the places mapped. It gives a range which is very broad. Zilpy, on the other hand, uses more info to make an estimate. It asks about number of bedrooms, baths and sqft. It is fairly accurate for one of our buildings, but is way off (by more than $150 a month) on the other. I am guessing that they don't update their information very well in some areas. Areas with more rental demand seem to get more attention by Zilpy; other areas seem to suffer. When I try to communicate with the site, their link is broken. Rentometer is probably a better choice, since they seem to know what the actual rents are for each building mapped.