Graphene is way more polished. It even features a browser-based installer. It comes with countless security and privacy improvements that can be non-trivial, but very nice (e.g. contact scopes). And they have an update process that wirks completely in the background, without any further action from the user. But of course the main downside is that you need a pretty expensive Pixel phone.
Lineage OS is less polished, but is compatible with many phones. It is also used as a base for many custom roms that alter the OS in specific ways.
I currently use both (with different phones).
Graphene is way more polished. It even features a browser-based installer. It comes with countless security and privacy improvements that can be non-trivial, but very nice (e.g. contact scopes). And they have an update process that wirks completely in the background, without any further action from the user. But of course the main downside is that you need a pretty expensive Pixel phone.
Lineage OS is less polished, but is compatible with many phones. It is also used as a base for many custom roms that alter the OS in specific ways.