If you absolutely need to share one server's filesystem, Samba tends to have more reasonable failure modes. If you absolutely need a truly distributed filesystem then AFS is your only real option. But really a filesystem is almost certainly not the right interface; you're almost certainly better off using something higher-level - maybe HDFS if you need to store file-like data, maybe a key-value store or a distributed queuing system if you're doing something more structured.
AFS (at least OpenAFS) is not "truly distributed": it has a single point of failure for read/write volumes. Yes, you can make read-only replicas easily and many large AFS users make good use of that, but it doesn't fundamentally solve the problem or fundamentally do something NFS can't.
Also you can avoid a SPOF in NFS with Isilon's commercial offering (which worked great in my experience, at least back when they were using an implementation based on FreeBSD's kernel NFS server), or potential Red Hat's HA setup.
Also, CephFS is an option too and avoids a SPOF by design. I've only run Ceph block storage but it's absolutely a real distributed system and works well.
