Where are the most hostels listed: TFThostels.com or hostelz ?

TFThostels.com aggregates hostels from Hostelworld, Hostelbookers and Hostelsclub.

I think Hostelz does the same, but also lets hostels list themselves independently of the booking engines. Since Hostelz has been around for so long, it has some hostels that aren't on Hostelworld.com or the other booking engines. An example is Rodos Youth Hostel.

Then there are the FUAJ hostels which aren't listed anywhere except for HIhostels.com -- which only lists HI hostels.

I'm just making a guess... there could be other factors... :)