In the early levels of Blitz, a team of Tidus (LF) Wedge (RF/MF) and Brother (need to be on the airship the first time, at least), is unstoppable. Ropp, who's on the Mi'hen Highroad, in the Al Bhed Shop, is one of the game's best defenders. Jumal, who's in Luca square (on the bench, by the bar) is a very good goalie in the early game.
If you've played enough to know the tricks, you can easily win with Tidus, and Wedge/Brother, and not need much other help. On the moonflow (I think Guadosalom side) there's a great defender named Miyu, she's also a very serviceable goalie until about level 30.
Brother and Wedge both falter late game. After about level 30/35 (far past what you'd play if you were just going for Wakka's stuff) their stat growth starts to slow down. Brother has the advantage of having 99 Speed, so he's always useful (even if his stats end up average), but Wedge becomes a liability. His stats supposedly go down once you reach level 85, but I've never been close to that.
The Kilika Beast (the worst team in the game) actually end up really good once you get to the 40's or so. With 3 of the best players in the game.
TL;DR. If you need a team Tidus, Wedge (Right outside Luca stadium), Brother (if you can wait til the first airship ride), Ropp (Mi'hen Highroad Shop) and Jassu work great. Miyu (Moonflow) can be the other defender, or your goalie until you find one you want. If you care about trophies, or Auron's Overdrive, you can backtrack to Besaid (takes about 2 hours both ways) after the Macalania woods, right before the temple there.
If you don't care about that, then no worries. You can backtrack to Luca, and grab Wedge, Jumal, and Ropp if you want an OP team.
Edit: If you're really into Blitz Ball, I've also got a few other recomendations. Not the best players, but some of the ones with interesting gimmicks, or just outside the team that everyone else uses. This time through the game I went with the Aurochs + Wakka and only; not optimal, but you save a lot of Gil for later.