Hmmmm, it really depends about what format you are asking for, standard or limited or both?
For Limited (draft), I have heard that black is one of the deepest colors on its own, typically followed by red. Also, for draft many people are not as much for green, stating that it is not as strong, especially when it comes to Fate Reforged. Blue has some decent maintenance spells, among other things, and again, works well with black. White has some good solid commons and uncommons all around, but is sort of stuck when it comes to strong removal.
For standard, I would say that you have to look at it in context with the other sets, as always! The dragons have provided a new win-con for the new Blue/Black and Esper control builds, and mono red has also obtained a ton of new toys.
I hope this helps! Someone please clarify or correct any erroneous statements of mine. =)