Whonix is isolated in the tor network. Everything in the OS is sent throw tor, therefore making almost everything encrypted. You can also install whonix on qubes OS making it even more Sacure.
Tails is a live operating system that routs all traffic throw the tor network making everything you post read and wright as anonymous as possible. When you shut of tails it wipes everything from the storage dvice you installed it on too.
Fedora is a good chose for privacy and is my personal recommendation if you want a red hat or cantos alternative. It has no problem with its privacy concerns and it would have the same for you to.
Archlinux has absolutely no updates. Arch Linux has only package updates but nothing on the OS. because of this there is probably no back doors that haven't been fixed yet.
Debian is a very good privacy focused operating system. With Debian being 100% open source we can tell what is collecting(witch is nopthing) and trust it in the mean time. There is nothing it collects so you can sit back and relax if that is something you are worryed about that.
You can not talk about any operating system that is the most secure with out mentioning Qubes OS. I use it on a daily bases and it works just fine. Qubes OS works by running all of the vms you could want and everything you need built in from the start.
In trisqule there is absulutly no propryitory software or fimware and uses linux libra (A very good GNU/Linux kernal)
Subgraph OS is one of the best when it comes to security. It stops any back-doors by sand boxing most things . All of it's trafic also gose truow the tor network leaving little to no room for man in the middle atacks.
if I could guide you in the wright way I would say you should go for Qubes OS. Not just because I think it is the best but if you do choose qubes OS it is a hyperviser system so if you want any of the above (witch it mostly already have) you can just install it.
