Second one...depending you your current devices. LineageOS is easiest (least secure (bootloader does not lock), decent privacy is no google apps but still pings sundar the creep decently regularly since OS is integrated into OS

CalyxOS is next but require specific device like pixel, strong AOSP security along with privacy (microG which pings google with it is say it is "anonymized")

OG for security and privacy GrapheneOS > improved AOSP security and an "arguably" improved privacy over CalyxOS (this is argement for MicroG over Sanndbox Play store you will see around here). MUST BE PIXEL (still pings google if you use GPS sandboxed, which you will as if you want any normie use cases)

There are other ones that might fit, so depending on you current device and threat model there other options.

If you not worried about state actors or crazy ex, LineageOS is fine to use while you test out degoogled life. But you really should move into other two on your next upgrade. people say calyx is the sweet spot, but after using both I am a GOS girl

Pixel is the device of choice for that. Consider used prior year model, bc fuck google ;)

PS i am very regarded so i will let pros correct this slop