Obligatory "There is not a single distro that's the absolute best for each and every one." disclaimer aside, my personal favorite is definitely secureblue for being a hardened-by-default distro that adheres to the 'immutable'reprovisionable, anti-hysteresis paradigm while enjoying a healthy stream of improvements pushed out by an active group of contributors.
Depends on your threat modeling. Though, unfortunately, none of the DEs/WMs on Linux offer perfect security; this even applies to a hardened distro like secureblue.
So, practically-speaking, it probably ain't great. But we aren't used to great anyways 😅.