Any owner of successful affiliate website can tell you that best conversion and commission are in local popular shops.
Demo: https://codecanyon.net/item/affiliate-egg-niche-affiliate-marketing-wordpress-plugin/21852757
Ronby theme is perfectly suitable for 6 niches (Agency Business, Medical, Restaurant, Fitness, Construction, Fashion Shop). Every niche is designed according to its purpose.
Demo: https://themeforest.net/item/ronby-6-niche-business-multipurpose-wordpress-theme/23555308