Strikes me as obvious. Everyone says Craiglist is the triumph of "worse is better," but the fact is that Craigslist is pretty bad. Maybe its competitors just haven't been offering the right kind of better.
Then there's the whole second tier of rental sites, such as eBay's rent.com, apartments.com, rentals.com and more. They are usually pretty to look at, but I found all their UIs to be difficult to use. That's where I took a simpler approach to search that I thought users would like better. Still, they get hits and engage in fierce search engine battles.
I still think there has to be a way to connect renters with rentals that's easier than what's out there. I do like rentHop's design at first glance as well. I do wish the rentHop team success. Anything that makes life easier is great.