I use Cloud, Tifa and either Yuffie or Cid. Because of Materia, it doesn't matter that much since the only differences between your characters will be the limit breaks. Cloud has Omnislash, Tifa has her limit attacks and Cid has the Highwind limit break. Highwind hits the enemies several times, although it only does little damage with each hit, at least when I played. Yuffie can use either Doom of the Living or All Creation, whichever does more damage. Barret can also be a good choice because of his Angermax and Catastrophe limit breaks.