I like my staff main best. I love being able to dish out damage, and heal as well. Also, the robes for staff mains are pretty sexy . (Although things like the level 80 HAIRPIN helmet..are terribly gay. orz)
I've only tried spear as main, so uh.. yeah. It's good 'cause you hit column wise, and you lower enemy ap.
I chose staff because if you have a monk, it gives kind of extra support. Staff users usually don't have great defense, so the monk helps. I've also always kind of had a thing for magic/healer/staff users.
I like the spear the most with the piercing ability and the -AP with lightning spear makes it great for slowing down or possibly stop the enemy from moving, and a bonus is being able to have a melee type of Stats rather then a ranged benefits from prophet.
the only thing i am sad about is the Spear main doesnt do a back flip when casting lightning spear Q_Q
Wish I had made a bow or staff main instead of spear. The -ap is nice, but whenever I think of a new formation it generally involves a staff or bow and doesn't include a spear. So, basically for the flexibility of being able to make new formations.