From what I've read, it hasn't really changed all that much. As ebony said, hunters are really good at quick, front-loaded burst, where warlocks are good at ramping damage once you get everything stacked up on the targets. So hunters would be better for trash and lower-level bosses, and locks would probably be better for bosses that take a long time to kill. And Unknowns is absolutely right -- being able to heal yourself while the DPS continues is no joke. Some fights are mechanically simple but just not doable on hunters due to the massive nerfs to Spirit Bond and Mend Pet. With the nerfs to Misdirect, the one really big advantage I liked about hunters (absolute control of aggro) is no different now than locks.

(Caveat: I haven't played in quite a while, so some specific changes might push the meter one way or the other depending on the fight.)