So i tested some services liek this site offers and i think this one is the best.
Here is a list of advantages:
- the howl service is free
- you can communicate to others with a message system,
- you can offer session to other or take their sessions
- support emails are answered within 24hrs.
- good looking ;-)
They build a system where you could vote for your holder (if you got one) for a completetd session, so the number of fake and bad holders is small. I like this fakt.