Are Number Two Portals Zoopla, Realtor.com and Domain About to Lose Their Places?

There has been a lot of talk about well-funded challenger portals in the industry recently and not a lot of positive press around the number two portals. Ed, Simon and Harvey take a look at number two portals Zoopla (UK), Realtor.com (USA) and Domain (Australia) to see which portal is most likely to come under pressure from challengers and which (if any) can challenge the established market leaders.