i'd imagine sid is far more stable than arch, but that is just my anecdotal experience.

plus ... ubuntu is debian. can't rly imagine why you'd want to base a new distro that is debian-based on something other than debian.

arch is a cool distro that I definitely respect, but I don't think it is appropriate to use for a workstation that you need unless you are on a filesystem that will do snapshots before package updates such that you can easily rollback. ie btrfs/zypper.