If assuming you just want a filler until you can get the Zon'ozz belt or BoE drop from DS I would say it depends on if your doin normal or heroic and how your mana feels. Disc mana vs throughput is pretty terrible this tier compared to some of the other classes. So a little extra spirit wont hurt ya. Can reforge the crit to haste or mastery.
If you don't have or want to get the ragnaros belt go for the raid finder version of the belt off of warlord zonozz at least(if not normal of course), those VP belts are both pretty shitful and the one off of dragon soul trash is one socket and a 10 int bonus with less haste vs the one off zonozz which has the most haste of any belt and 2 sockets and a 20 int bonus