I've tried the rest, this is the best (so far).

I’ve tried offerings from nrelate, Shareaholic, and others with limited success. I’ve been using Related Posts by Zemanta for over a month with no issues. I like how it shows up in my site’s RSS feed, the mobile layout, and how it can be manually added to post templates in order to control where it appears- see https://support.zemanta.com/customer/portal/questions/1062371-change-plugin-location-at-the-page-

I’ve not had time to push it to the limits. I hope Zemanta remain consistent with their support.