Elder gets the most possible charisma for shamans, maybe go ogre for the punch CM, a little extra damage every 6 seconds, might help with soloing.
Mystic is best for raiding simply because it gets a very nice debuff.
Pet path or Debuff path, normally I would just say Debuff because they screwed pet path by giving all shamans the same et at 60, a level 50 primal spirit or something of the sort.
However, with the new 60 epics coming out, shamans will now have a more powerful pet if they are pet path..
So Soloing, I would have to say Pet path, as you have a higher level pet throughout the game, it will obviously do more damage..