I go with two sabers - first cause I can't decide which color to use (silver or viridian, so I use both) ... and because I can have more interesting combinations of crystal addons. I was playing as Sentinel / Jedi Master ... and my goal was to boost my Wisdom as much as possible ... each of my sabers had a crystal that increased it (pet crystal in one, and some other crystal in the other) ... in addition to a boost to other stats. With just two crystal slots, and with the pet crystal, there is only one extra that I can put in ... not as much fun.
The staff does look better in a fight, especially after seeing Bastila use it in K1