I use btrfs, and the main reason I don't consider zfs instead is that zfs doesn't use the regular linux fs page cache. That and the fact that I use latest mainline kernel, so dont want to have to deal with kernel updates breaking zfs or tanking its performance, as when it lost access to the simd functions. The main feature I would want from zfs would be tiering, which can be gotten from btrfs on bcache, which is what I will likely use in the future. I think there was some issue with adding disks in zfs too? Don't exactly remember about that.