There are a lot of factors to take into consideration ...
What is the target niche of your product/service?
Are you looking for a 'full service' JV Broker (doubling as a JV Manager), perhaps even a Product Launch Manager, or simply a 'connector' to work with an existing JV/Affiliate Manager?
Do you need them full time, or just during a new product launch or affiliate program announcement phase?
Or is your need more of a rolling launch where you'd like to connect to one new JV partner at a time, setting up a special offer +/or perhaps a live call or webinar unique to their lists?
I know many JV Brokers, JV/Affiliate + Product Launch Managers ... but they often specialize in the areas mentioned above and more, so it pays to save time and look for one that answers your specific needs.