[mmooss]

Greatly improved privacy and security and end-user control of your phone and its data. In those areas, possibly the best option, though iPhones might be better in security (not necessarily the other two areas) - Apple has a slightly bigger budget and a few more engineers, and directly controls the hardware.

[strcat]

GrapheneOS exists to greatly improve the privacy and security of an existing open source OS project. Android Open Source Project has good privacy and security as a starting point.

Pixels provide strong hardware and firmware security. Pixels have made multiple significant hardware and firmware level improvements based on recommendations by GrapheneOS. GrapheneOS now has a hardware partnership with Motorola Mobility which includes working with Qualcomm. It isn't only a software project.

Regularly leaked data on the capabilities of Cellebrite show they have the least success with GrapheneOS by far despite specifically hiring for it based on their job postings.