The whole first section of the post (under the title How do you find the most popular publications on Medium?) is devoted to that and includes the link to one such place, Top Pub, that lists most of the publications by genre as well as the number of followers. I was able to find the link to that on the first page in Google when I googled “top publications on Medium.”

Not to mention that 90% of posts you see on Medium’s homepage are published in various publications. So finding a publication on Medium that fits your interests should be relatively easy just by reading stories and paying attention to which publication published them.