Just a thought:
I really don't see an edge either by NAS or SAN storage device without considering or understanding first the other entities of an Infrastructure.
I mean.. if your infra involved with low or high network performance. Or your servers maybe an entry-level, midrange, or high-end, this clearly will influence the performance of your storage device.
If you have at least a midrange server which has a fibre channel bus architecture(IO comm channels/network/host adapters) then it will best fit to use SAN. Because SAN fits or maximized with this. On the otherhand NAS will be most likely be suitable in an infra where communication/network high performance become a standard(using Gigabyte Ethernet network systems/fibre optics).