best size for featured image

Hello,

There is no ideal image size I can recommend. You will have to assess the containers and thumbs you plan on using on your site and the post templates as well. If you use post templates that use the full-size images like http://demo.tagdiv.com/newspaper/td-post-2015-awards-all-of-the-best-and-worst-moments-from-the-show/ then a full HD image is required. If not, you need to inspect every element, in particular on the homepage. If you use big grids, your images must be at least the size of the big grid container. Otherwise, they will not fit inside and not display correctly. Here is a list of all thumbs used in our theme:
https://forum.tagdiv.com/theme-thumbs/ also -> https://forum.tagdiv.com/thumbnails-vs-featured-image-size/

Hope this helps!
Thank you!