Top WordPress Commercial Themes in ThemeForest.com
2019’s Best Selling WordPress Themes – updated weekly
https://themeforest.net/popular_item/by_category?category=wordpress&ref=_themeart
http://www.wpexplorer.com/wordpress-themes/
Top WordPress FREE Themes in WordPress.org
https://wordpress.org/themes/browse/popular/
Best Free WordPress Themes:
http://www.wpexplorer.com/top-free-themes/
Resources:
Best WordPress Themes Tutorials
https://www.wpbeginner.com/category/wp-themes/
Neil Scott: Improving the User Experience of your WordPress sites
https://wordpress.tv/2019/04/11/neil-scott-improving-the-user-experience-of-your-wordpress-sites/