Azteeg Pro or Duet with motor expansion?

I'm planning to get a kraken in the near future, and in order to use it I will need a board with more motor inputs. I was wondering what are the advantages and disadvantages of the Reprap Duet and the Azteeg x3 pro. Also, if there are any other boards currently out that can handle 4 extruders, what are they, and what are their advantages and disadvantages?