Could you explain the criteria exactly?
1. If "/hdd" points to something that exists, it will use that.
2. If /media/hdd exists (may be symlink or mountpoint), it will use that.
3. If there are non-removable disks, it will use the largest(*) one.
3. If there are (other) local disks, it will use the largest(*) one.
4. Otherwise, it'll use the largest(*) available mount.
(*) Currently the formula for "largest" is: (total size) + (free space).