I sorely miss DivestOS for this purpose, but I'd consider CalyxOS (development sadly on pause) ~~and iodeOS~~ as runners-up. /e/OS got caught sending voice-to-text data to OpenAI, so I'd stay away for the time being.
edit: sad to see that iode has a freemium model on some of its features. see replies for more nuance on the /e/OS situation.
LineageOS will get the most years of support out of the most devices. While leagues ahead of Android for privacy, bear in mind that it still isn't airtight with regard to the occasional piece of telemetry data sent back to Google. It's about the only thing that can keep one of my older Pixels somewhat up-to-date.
LeOS is like LineageOS with all Google telemetry stripped out, but only in GSI form (no builds optimized for specific devices), so YMMV with hardware compatibility. I have this on my Samsung tablet.
I've also heard about Volla Phones (with VollaOS) and Brax Phones (with iodeOS or Ubuntu Touch), but haven't taken a serious look since the screen sizes offered are too big for me.
I might try out a Linux phone next, but the relative lack of battery optimizations and edge-case issues leave me a bit hesitant. Also, check out detailed comparison of the common Android ROMs with regard to privacy and security: https://eylenburg.github.io/android_comparison.htm