These are top and recommended Affiliate Extensions For Magento Ecommerce

1) Landofcoder Affiliate Extensions
This is a perfect extension for you to create your affiliate program. As you may know, affiliate marketing is one of the most important marketing tools for selling online
Link: https://landofcoder.com/magento-2-affiliate-extension.html

2) Marasvit Affiliate Extensions
Launch fully featured affiliate programs for your store with the Magento 2 Affiliate extension! No need to use third party services and pay them fees anymore. Drive more sales from alternative channels and let your affiliates earn additional money.
Link: https://mirasvit.com/magento-2-extensions/affiliate.html

3) Affiliate Pro is one of the best affiliate extensions on Magento 2 market with many advantages:
* Pay commission by sales
* Create multi programs
Link: https://www.mage-world.com/magento-2-affiliate-extension.html

I will suggest you magento 2 affiliate extension https://amasty.com/affiliate-for-magento-2.html. Run full-scale affiliate programs on your website to effectively drive sales from alternative channels. Provide affiliates with promo materials and detailed stats reports. Easily manage affiliate accounts, regulate commissions and track withdrawals.
Launch affiliate programs based on cart price rules
Set a specific commission type for each program
Configure discounts and payout requirements
Use a great variety of promo materials
Manage affiliate accounts and transactions
Mobile optimized frontend

I will suggest you check out this extension Magento 2 Refer A Friend - https://www.fmeextensions.com/magento-2-refer-a-friend.html

Useful Features
1- View Details like Referral Links and Earnings from ‘My Account” Section
2- Allow Social Sharing
3- Set an Expiry Date for the Rewards to Avail
4- Gove Reward for Registration
5- Set Targets users fro Registration
6- Reward referrer infix amount or in Percentage