The optimization and the speed of WordPress websites is a big issue.

Main reasons of low performance website:

• Big images (probably you are using high high quality images not optimized for web)
• Many plugins (they load even if you don’t use them).
• Theme full off options that you don’t use.
• Many Google fonts.
• Server resources are limited.

Some of the previous issues you may need to solve manually, but if we have to mention the best plugin to optimize your WordPress website speed, we should mention: Autoptimize.