If reliability really is your prime concern, I would seriously consider going with a commercial Linux (RedHat, SLES). They're engineered to provide consistent, stable performance over the course of years. You won't get the latest packages the moment they come out, you don't want to do that if reliability is your prime concern. But you will get backported patches into the versions you are running so critical bugs will still be fixed. And if things do break, you have a support contract to fall back on to make things right.
As for file-system, they all perform reliably. The difference is in how they behave when things go wrong. If you're using commercial Linux the latest filesystems (btrfs, ext4) don't exist on those platforms quite yet; SLES has btrfs in an experimental mode, which you don't use if you want reliability. Your choices are, pretty much, ext3, xfs, and reiserfs.
If you don't have 100% (or at least five-9's) confidence in your power environment, or for some reason are not opting for the battery on your RAID card, ext3 is probably your better choice. Due to how it works a sudden power-loss is less likely to cause data-loss than with XFS. But if you do put that battery on your RAID card, XFS journal transactions are less likely to be lost and that edges me towards XFS as your filesystem of choice.