Do not select an agent based solely on the agent fee; it comes second to quality of service.
Use an estate agent that has been recommended to you personally or one with whom you have worked in the past.
Before contacting an agent, run a few searches at your areas of interest. Use the Find Agents search engine in your areas of interest, run some property searches and identify estate agents with good quality listings in those areas, check their profiles, see how they advertise the properties they manage.
When you contact the real estate agent, ask what marketing he will do on your behalf.
Remember that it is harder for potential buyers or tenants to find your property, if it's not at the Spitogatos network of sites (over 3 million users / month)