Problem is, direct additions or reductions to your base delay on a weapon affect your TP per hit. Not sure the exact calculations but 3% could potentially screw up a 6 hit build. If not, then that's just dandy; although more STR or acc would be ideal.
Accuracy can be found on any number of other pices of gear, haste can only be found on a few. Considering how much NIN benefits from haste, I'd always prioritze haste.
Edit - 7-8 times out of 10
Just to point out, there are plenty of jobs that benefit more from haste than nin does, just every DD benefits from haste a bunch.