I think it depends on maintainer of the device. For me personally, LineageOS has broken a basic workflow like having Signal voice/video call. None of the IM apps are able to pick audio from microphone on my device (and various other models as well) due to a bug in LineageOS for almost 6 months. I regret installing it.

I use graphene because I just like its way stricter security features, such as randomized numbers on the keypad when unlocking and it not having any Google services by default

But if you dont care about that and you would rather use MicroG (which is a little project that still runs at root access, but dosent send as much data to google) instead of G services just being sandboxed you can just as well use linaege

Also, linaege is a Team of volunteers that maintain many phones, as grapheneOS only makes Roms for the Google Pixel Series, so all their effort is towards the pixel phones. But as far as I know Graphene only maintains the Roms for phones that are still maintained by Google themselves, only giving a year or so extended support, but I dont know how long the Maintainer(s) that support the Pixels will maintain the Rom

Graphene has a bunch of features that you may or may not agree contribute to privacy over all (funny since it only operates on Google’s devices, that is, devices designed by a US enterprise).

LineageOS has some little QoL features but otherwise keeps it very AOSP. The most prominent difference is the dependence on specific device maintainers, meaning that some devices may get stuck on A13 while others may already have A14 or 15, though imo it’s a small price to pay for having a modern OS on a 10 y/o phone or tablet. Graphene only provides support for Pixel models that have security updates, so you will end up with LOS if you’d like to keep using your Pixel 2/3/4 etc.

LOS can get rid of the pill at the bottom of the screen 😏