Probably truenas, recommend true and scale as it’s Debian based not bsd like core is. Makes running VMs much easier and way better hardware compatibility in theory!
Definitely not the "easiest", but this is what I use.
everyone says Debian but they don't say
how it started: Raspberry pi
how it's going: proxmox
Debian with docker
easiest/most reliable OS for a small homeserver
Debian stable, skip docker / snap and similar crap, add unattended upgrades.
If you don't have any experience, then probably FreeBSD imho; Follows unix philosophy, stable, built-in support for ZFS, dns caching, NFSv3 & NFSv4, used as the base system for stuff like OPNsense, freenas and a bunch of other stuff at one point in time or another.
And it's really well documented.
If you already have a set of linux utilities or a certain distro you really like then go for that. But it's almost always going to mix-up user and system installations along with needing to learn new stuff for every distro and hoping it's stable with all the different package managers you will need.
You could have a look at CasaOS.