This is an old post but here are my two cents.

LineageOS supports much more devices. It’s what I personally use. It’s security very much outclassed by that of GrapheneOS. However, to be honest I don’t care all that much. I’m not a journalist or targeted person. And I, personally, like to root and “pimp out” my device with kernel mods and the like. While all this CAN be done on GrapheneOS, it sort of defeats the purpose of having GrapheneOS. It’s supposed to be a secure, locked-down fortress.

In short, if you want a super secure, de-Googled device, then GrapheneOS. But if you want a Googled device you can do a bit more with, and really make yours in every way, then LineageOS.