Just the utility that a lock brings with gateways (evetho they are getting nerfed to once a minute) and health stones is pretty awesome. Being able to replace almost any buff with a hunter is awesome too but in 25 man's that isn't really needed since there should be no missing buffs at all.
Even assuming the hunter buffs to signature shots in light of Readiness's removal will bring them in line with the other dps this tier, Warlock provides much greater utility. If you enjoy both classes equally, and are equally skilled at both, I would go with the warlock.
Otherwise, for anything other than bleeding edge progression or a very hardcore-minded guild pushing H content within the first few weeks of release, just go with whatever you enjoy most or are best at.