openSUSE Tumbleweed because it is the most reliable rolling release distribution I have used. I love the automatic btrfs snapshots and wish other distributions would have them setup out of the box.
I haven't had any problems with btrfs. There have only been a couple of cases where I used the rollback functionality and it worked as expected. I have also been using a Synology NAS with the btrfs file system for several years without any problems.