I ran Cyanogen on my cell phone
Those who don't have (and don't want to build) the technical skills required to make any of this themselves are, as of today, probably be best served with /e/OS. I've never used it myself, but from what I hear and what I can tell, it provides a complete “everything just works out of the box” experience.
A bit of background as to what /e/OS or Cyanogen even are: There is the Android Open Source Project, or AOSP. When a manufacturer produces a phone, they take the AOSP and add vendor- and device-specific modifications; the result is colloquially called a ROM. Unlike with desktop operating systems, where the same DVD can install on any computer, ROMs need to be device-specific to function. Because nobody else produces a ROM for a specific device, costumers are effectively forced to buy a new product when the old one stops receiving updates – which is entirely a choice of the manufacturer, who simply stops making updated ROMs.
This annoyed many people, so they started making their own ROMs. One of those was Cyanogen, which is now called LineageOS. It is the most popular, and gets modified further to give rise to yet more variants (derivatives). To use an analogy: “There's the car model XYZ, but derived from that there exist the XYZ Racing and the XYZ Double Cab.“ The most important LineageOS derivatives are: Lineage For MicroG, /e/OS, iodéOS, and DivestOS. Besides those, there are two more major ROMs based directly on AOSP (like Lineage itself): CalyxOS and GrapheneOS. For those who have (or want to build) some technical skills, GrapheneOS is probably the most interesting choice (if I bought a new phone today, I'd probably install Graphene, but in reality I still run LineageOS).
Because installation ROMs are device-specific, not every device is supported; so when intending to do this, it is important to check the ROM website and purchase a supported model – and in either case, listen to Cassius, when he said:
I favor free open source software whenever possible