Better for what?
zfs and btrfs are both more advanced filesystems than ext4 but more advanced means more features, not better performance.
So the first question is, do you need/want those features. Things like snapshots/snapshot replication, built-in raid, transparent encryption and compression, etc, etc.
If you do, than for me it breaks down like this. zfs is slightly more complicated than btrfs but also more reliably and has some features that btrfs doesn't such as zvols. However, it is also out-of-tree so needs special modules.
I guess the short answer is, for my needs, I prefer zfs but there is no "right" answer here.