The OS is not very relevant to the Pixel. Compare the Pixels you like that are new (GrapheneOS drops support as models become older flagships, I think for security reasons) and get that one. IIRC, currently only Pixel is allowed, because the bootloader can be opened without rooting the device.

https://grapheneos.org/faq#device-support

Unrelated to bootloader or rooting. Pixels are the only phones that adhere to the device requirements that are listed in the FAQ.

https://grapheneos.org/faq#future-devices