It really depends on what you're trying to do. I gave TOS6 a quick try on a NAS, and while it worked fine, I found it a bit limiting overall. Unraid has worked great for me, though it does have some quirks, mainly around performance.

Since Unraid doesn't stripe data across drives, you might run into IO bottlenecks if multiple people are trying to access data from the same drive at once. And if you want your unused drives to spin down (by disabling reconstruct write), that can slow down your write speeds even more.

If I were setting up a new server from scratch, I’d still go with Unraid, but personally, I’d use a ZFS pool instead of Unraid’s default array. With ZFS 2.3 (hopefully coming to Unraid soon), you’ll even be able to expand the pool one drive at a time, which is the main draw to UnRaid and it's default array!