These are top and recommended coupon code extension for Magento 2.

1) Coupon Generator by Landofcoder
Coupon generator extension for Magento 2 is a useful tool that helps create the coupon codes for you through email templates, variables, and rules. It allows sending the coupons to a specific customer group quickly. Besides that, it also enables sellers to follow the sale campaign as well as manage the coupons conveniently.

Link: https://landofcoder.com/magento-2-coupon-extension.html

2) Coupon Generator & Importer by Mageplaza
By being aware of the importance of coupons for every e-commerce store, Mageplaza launches Magento 2 Better Coupon extension. Not only does it help save more time for admins in their business but it also helps enhance the customer purchasing experience on the store. Additionally, thanks to this module, you can create coupons codes quickly as well as easily send them via emails.

Link: https://www.mageplaza.com/magento-2-better-coupon/

3) Coupon Generator by Aheadworks
Magento 2 Coupon Generator is the best choice that allows admins to create, delivery, and follow individual coupon codes. It is totally compatible with any 3rd-party extension. Besides, using this module, store owners can set the rules for the coupons as well as the expiration date for them. Thanks to this, your revenues can improve dramatically.

Link: https://ecommerce.aheadworks.com/magento-2-extensions/coupon-code-generator