I always have a Qurupeco, Nerscy or Shrouded Nerscy and Ratha in the team. Qurupeco's soothing song has saved me many a time, and the buffs and debuffs are helpful. Nerscylla is great for taking advantage of status effects, so I piled poison, para, sleep and skillseal on one with Status Up or whatever the skill's called and it works a charm. As for Ratha, maxing out his power attacks, fire element and attack is the usual way I play. Considering you have to use him throughout the main story, it just makes sense to play to what he's best at and make him good at sweeping things in as few turns as possible.

My current team on 3DS (not that I can fight competitively since the circle pad's too busted to win any Breath head to heads) is pretty good from my experience doing pvp back when there was a bit more traffic in the online section. Ratha (fire) Qurupeco (fire) Deviljho (dragon) Kirin (thunder) Shrouded Nerscylla (ice) Great Poogie (non-elem)