I use unraid. I'm pretty happy with it for the most part. Its true you can just roll you own, but I don't really have time to learn everything these days. The hardware NAS units are popular and look like great products to me but I felt like unraid on junk hardware gave me some tinkering flexibility.
I'm not adverse to linux, just have spent minimal time in it other than occasionally using a linux diagnostic disc to test a pc. So I'd want something that is pretty straight forward with its instruction for installation and maintenance.
I dont need RAID for this. This units will be a jbod extension of the WD NASA enclosure I have for my media pc. It will almost exclusively be used for in home streaming.
I do like the way unRAID handle's drive pooling, and being able to use disks of varying sizes is a nice bonus for people doing ad hoc builds. The ZFS-based distros like FreeNAS and NAS4Free are a bit too rigid that way, IMHO.
FreeNAS has Plex Jails you can install via web gui.
unRAID actually has full virtualization support via an integrated version of VirtualBox. But if you want to go that route, I'd wholeheartedly recommend KVM on Linux instead.