Comparing products in the multi-vendor marketplace. it's really helpful to customers to choice right/cheap product in your marketplace. If you are looking to introduce add-to-compare feature here. And I explained how to do that.
YITH WooCommerce Compare plugin is a common best supportive plugin for WooCommerce. So this will allow users to compare products of your shop. All products are saved in one complete table. where the user can see the difference between the products. This plugin will compare the attributes of multiple products. Also, there is a widget available to list the products. And users have added, where you can manage them. Also, you can simply customize the compare table with your style, by editing the specific template.