The only advice i can give you is get Brother(One of the Best)
also for goal keeper get Nimrook from the al bhed team...
But kappa is pretty good too so you can choose..
Here's my team line up:

LF - Tidus
RF - Vilucha(he's in the house at Besaid Village)
MF - Brother(Pilot of the airship)
LD - Ropp(he's in the Travel Agency at the Mi'hen Highroad
RD - Wedge(He's in the Main Gate of Luca Stadium)
GK - Nimrook(He's in the Corridor of the Airship)

I suggest that if you get to your highest level ,use those line up...

It's only a suggestion though