Lately I've been encountering some slowness on my site and those of my clients and so, I made some research on the best types of plugins on WordPress and I came up with a few. They are:
1. Shortpixel.
2. W3 total cache (premium).
3. CDN (yes, not a plugin but highly needed).
As the week goes by, I'll try to update this thread on how to setup each plugin configured with a CDN.