For the people that are gearing up in LFR and the like it seems that for warlocks the Jin'ya, Orb of the Waterspeaker staff is btter than the Loshan, Terror Incarnate MH + Tornado-Summoning Censer OH.
You can see here that the staff will give
+453 Haste (1.07%)
+2 Spell Power when compared to the MH+OH.
MH + OH will give
+104 Crit (0.17%)
+306 Hit (0.9%) when compared to the Staff.
The overall secondary stats gains/losses both workout to be a total of 1.07% on either end. However you gain a minor spell-power gain on the Staff. Also given the scaling factor of Haste vs Crit, the 2h seems to benefit Afflic and Demo more than the respective MH+OH combo. If you rolling Destro (which is very useful for some fights like Elegon) or looking for ways to make up the missing Hit% you may favor the MH+OH combo. I personally believe that .9% hit is better off reforged from crit from other pieces of gear you may have.