Thank you all for your contrabutions.
I have now chosen my agent having whittled it down from a selection of three.
It is really interesting to see the different approaches adopted by different agencies. Customer service even at this early stage is also, revealing shall we say.
The agent I have chosen is 'local' but very Social Media savy, no contract, 15% commission and any amount of owner bookings . The risk for me is I'm outside of their current geographical area (but one they very much want to move into).