I never tried PopOS, but I would never suggest Ubuntu. Manjaro is easy, updated, there are many people using it, offers large number of software, works well with Nvidia and other propietary drivers (the thing that generates issues for new users, usually). I know people think they had “security” problems, but they always explained what happened, and they just had a bad contract with the CDN service and a misleading error message in pamac, that didn’t impact the security of the user.