Best NAS is the one you build based on your requirements. Then use FreeNas or Unraid as the operating system. I myself use Unraid and love it. Just do some research as to what would best fit your needs.
And then you’ll get some idiot coming along and tell you TrueNAS Core or TrueNAS Scale (about to release) is better
Even though I really like the QNAP hardware, their software is getting worse imho.
I’m currently battling a problem where I experience a 50+ % loss of Disk I/O performance. From 1.2 GB/sec → 500 MB/sec ?
I’m giving them time to resolve because I’m not the typical user but, if it doesn’t resolve, I will load TrueNAS Scale on it without hesitation.