Hmm mystery or horror. So here's the thing, I love love love horror, but looking at my stats, I read way more mystery novels than horror. I think that's because I love a well crafted mystery and also the mystery genre does a great job with setting up characters you love and a series you can follow. I can only think of a few horror authors that actually follow characters through multiple books (King and Koontz) and I don't think it's a thing that most horror authors do.
For me I think that a well written mystery like "Where the Crawdads Sing" just stays with you. You give me well developed characters, a tight plot and then a mystery I can sink my teeth into I am happy. I am the same person that lost her mind after I read my first Agatha Christie novel and went I must have more! I also have been reading a lot of mystery series like Inspector Lynley, Inspector Armand Gamache, Prey, Kinsey Millhone, and Bosch series for the past two years.