Yeah, I chose CalyxOS over Graphene because it seems to me that CalyxOS focuses a lot more on usability (thanks to it’s MicroG support) than Graphene does. Graphene has likely improved on that front thanks to their sandboxing GSF approach, but it used to be slower to open apps and overall a bit less snappy due to the security features it enables. Plus, the team behind CalyxOS is fantastic, great guys who believe in what they are doing. Meanwhile, the leader of GrapheneOS is a bit… Psychotic, although he did recently step down after Louis Rossman called him out.
For ProtonAOSP, that’s basic just stock android. However, I’m unaware of it comes with either MicroG or Google Services installed. If it doesn’t, then you’re gonna have to figure out how to get support for apps either by flashing MicroG along with it, or be stuck with Foss app only. If it comes with Google Services, then it’s basically no different than stock Pixel Android at that point, which you might as well stick with to gain the full benefit of the Pixel device.