Every style of music, from mainstream to the most niche subgenres
The easiest way to sort down to a single style of music. Every station carries a few genre labels, so jumping from one list to another often surfaces familiar names again. A style with only a handful of stations just means few have been labelled with it, not that the music is not out there. If you are looking for something very specific, the niche subgenres towards the end of the list are usually where you find it. The broad categories at the top are the right place to start when you just want a big pool of stations to wander through.
Sometimes the right filter is not a genre at all. If you are looking for something to match an activity or a time of day, the Mood page groups stations by the feeling rather than the style. And if the genre you like tends to live in a particular region, starting from the Country page and narrowing down from there often gets you somewhere faster than the other way around.