exFAT is slow, that's my beef with using it and it doesn't appear to show any true advantage over using NTFS. You can't interface exFAT with any MS OS pre-XP or if XP machines aren't on SP2, or if Vista users aren't on at least SP1 so I would suggest NTFS. exFAT is in theory more efficient than NTFS but tests show otherwise, I have a 16GB eSATA flash drive and it takes extra minutes to move data to and from it in exFAT.
One of the inconsequential benefits is how it has the tendency of keeping data less fragmented because flash drives can access data anywhere on the flash memory regardless at the same time.
I use my flash drives to move data between 3 different platforms, Linux, OSX and Windows XP/Vista/7, NTFS will be the best choice in that scenario. A lot of OSX users out there don't use updated builds, only Snow Leopard with the latest release will read exFAT, those on Leopard and Tiger won't.