Hi. I have a few apartments in Barcelona/Spain that I  rent short term
to tourists . Most of my clients come  from the UK , some from
Scandanavia and a few from the US. Currently I advertise on
www.holiday-rentals.com as they claim to be the biggest such agency in
the world.
    I would like to find out more  on other agencies and which ones
deliver the best results for their advertising dollar. There seem to
be hundreds of such agencies and its hard to know which are 
effective.
     Perhaps there are internet forums that discuss this topic or
sites with  ratings of such agencies?

Declan