When it comes to booking interview guests, conventional wisdom says to book the person most conversant on the topic you're covering. But what if there are a few guests who can get the job done? Who should you chase? If all guests are equal on the surface, look at them from a marketing angle: Who will help you make the biggest splash? It's almost always going to be the person who's most active on social media.
...and that doesn't always mean who has the largest number of friends or followers. Anyone can amass a lot of names on a list; you'll want to identify the person who's most engaged with his/her audience. That's a person who will gladly share a link and talk about your show and the interview you did.