Using a cache system throws a wrench into testing since it will significantly improve the load time of your website and change how assets are loaded. I like WP Rocket for managing my page cache and many other speed settings, and I heartily recommend using it in conjunction with whatever social sharing plugin you use.
In my testing, I found that Social Snap works best with WP Rocket and the other caching options I've tested. It's a little better optimized, and it handles some things like social sharing counts a little better. If you need to pull data locally, it's faster than using an API, after all. Also, if you only want to use the share buttons with no sidebar, or the sidebar with no share buttons, it will only load the necessary code for those sharing elements.
The icons for each of the social media networks account for the bulk of the assets being loaded in these plugins, and Social Warfare uses a much heavier icon font family. Social Snap uses modern SVG images for their widgets, which can, in turn, be lazy-loaded and optimized. It's much more efficient to load the visible social media icons than load the entire icon font family containing the logos of all social media platforms. Social Snap wins here, and I had a definitive performance increase after switching.