Digital BW, The Print

Some third party workflows like QTR will have their own instructions
for which intent to use, but for a native driver and ink setup, I
wouldn't lose sleep over which to use. The main function of a
rendering intent is to determine how out of gamut document colors are
handled by the printer. If you're printing grayscale, or even tints
and split tones, exceeding printer gamut should not really be an
issue.
-- 
amadou diallo
Author, Mastering Digital Black and White
www.masteringdigitalbwbook.com