Even though AP and crit is lower, it is more than offset by the higher dps and hit rating.  Go for the knives.  If ur fury spec, the hit rating for the knives is especially helpful.  For prot, also the knives.  For arms warr, the tiny bit of extra crit and AP on Hemet's gun might be usefull, but only margnially so.  In general, the knives should put out about 5% more ranged dps.  But as a warr, I only use these things for pulling.