When searching for a podcast to subscribe to, showing the closest match is good, but it's almost always counterproductive to show podcasts that have only 3 subscribers at the top, even if the name closely matches what I searched for--because on average, almost nobody is looking to find such a podcast. (Only three people chose it so far.)

Instead of having to choose to sort by "Relevance" or "Number of subscribers", the default sort should be called something like "Best result".

This default sort would use the weighted average between these two factors: I suggest the total weight (needs testing/tuning) would be:
1/3 * log(subscribers)/16 + 2/3 * search_relevance

I chose that number so the most popular podcasts have a popularity score of around 1. I'm also assuming the best search relevance would be 1. Scale as appropriate.