I run Debian with zfs. Really simple to set up and has been rock solid for it too. As far as I can tell all the issues I've had have been my fault.
ZFS looks like it uses a lot of RAM, but you can get away without it if you need too. It's basically extra caching. I was thrilled to use it as an excuse to upgrade my ram instead.
Mdadm has a little more setup then zfs, as far as I'm concerned. You need to set your own scrubbing up whereas zfs schedules it's own for you. You need to add monitoring stuff for both though.
I've considered looking into the various operating systems designsd for this, but they just don't seem to be worth the effort of switching to me.