Found the following summary of genre sales (by a group marketing marketing services for self-published books, duh!).
You're at the starting gate, ready to self-publish your book. But how do you know if you have a winner? We at Self-Publishing Relief know that while some genres seem to enjoy unbridled success when self-published, others fall behind in the race for sales. Take a look at the top-selling genres in self-publishing to find out where your book fits in:
Win: Romance, Sci-Fi, Fantasy
Romance, science fiction, and fantasy books are the best-suited for self-publishing. In fact, half of the e-book bestsellers in the romance, science fiction, and fantasy genres on Amazon are self-published! Readers of these genres are more likely to share recommendations via blogs and community forums, and their clearly defined interests make it easier for authors in these genres to target their book sales marketing efforts.
Of these three genres, romance books make up a whopping 40% of the market share on Amazon e-book sales. And if you think romance sells so well because it's erotica—not true. Only 1.2% of Kindle sales are erotica. The romance genre actually covers many other types of romance novels—even Christian romance. You're in good company if you love writing romance novels, whether they're steamy or not!
Place: Mystery, Thriller, Crime
Of the Top 100 mystery and thriller Kindle sales, 11% are self-published books. While not as popular as the romance genre, self-published mystery, thriller, and crime books still sell extremely well.
Nonfiction books are also good choices for self-publishing. They make up a smaller percentage of the market, but readers are often happy to pay more for a nonfiction book. So even if you sell fewer books than fiction writers, you'll still make a decent profit because you can charge more for each copy.
Self-published literary fiction doesn't sell as well as genre fiction does: This category makes up only 2% of all Amazon e-book sales.
So is every non-romantic book destined to fail?
Don't let generalizations about which books sell best discourage you from self-publishing your book, whether it's a romance, a mystery, or even a western! It's important to stay true to your unique writing style and vision—forcing yourself to write only for the market will show in your work, and disappointed readers will notice. Instead, you might want to consider adding a little more romance to your mystery novel to create some crossover appeal, or querying agents for a little longer before starting down the self-publishing route.