LiteSpeed Cache is a free caching plugin, and it is the best choice if your host runs LiteSpeed web server, which a lot of shared hosts do. In that case it can cache pages at the server level, which is faster than a normal WordPress caching plugin. Even on other servers, it still works as a solid page cache, and it adds a lot of optimisation tools in the same plugin. It minifies and combines CSS and JavaScript, lazy loads images, converts images to WebP, and optimises them when they are uploaded. There is a database cleaner for old revisions and expired transients, and an object cache option for sites that need it. The settings page has a lot of options, which can look daunting at first, but the default presets are sensible, and you can turn features on one at a time. It is free, it is maintained by the LiteSpeed team, and for a site on a LiteSpeed host it is hard to beat on speed for the price of nothing.