Speed: Show me a BTRFS machine that beats the ZFS machine I linked to.
Data integrity: Show me that BTRFS does offer data protection (I have showed research papers where they tried ZFS and the researchers said ZFS detected every injected error, and would have corrected every error if they used raid. In the study, they only used single disc).
Functionality: BTRFS lags behind here too. BTRFS is still in development phase. For instance, ZFS has dedup. BTRFS has not.
So, ZFS gives more performance, provenly data protection and more functionality - am I wrong when I claim ZFS to be better? And best of all, you can download ZFS today and use it. It is free. BTRFS, it is not ready yet.
When a filesystem is released, it takes at least 5 years before it is let into Server halls. There are too many bugs. If you crash a kernel, you loose a days work. If you crash a filesystem, you can loose several years of data. Filesystems are far more important to get bug free than a kernel. No Enterprise server hall will allow BTRFS in 5 years after releease of v1.0.