If you're only looking to play blitzball up until you get the Jupiter Sigil and then stop forever, then I'd definitely recommend that you sign Durren as your goalie as he starts of with a high catch stat which increases a fair amount in early levels. I kept Jassu in defence but replaced Botta with Ropp, as although Botta is the better tackler, he doesn't have sufficient EN or PA to get rid of the ball after a tackle. As for the rest of the team, they were good enough as they are. Datto may appear to have a too low SH but this does pick up, and he also becomes extremely fast. I kept Letty in midfield for ages, but Brother is your best choice there.

If you intend to keep playing afterwards though, then if you have signed Durren make sure you get rid of him pretty soon after his CA reaches 30. Try to get hold of Nimrook if you can, because he remains the best goalie in the game throughout; whilst Durren's CA hovers around 30 for ages before slowly falling back to 24; and none of his other stats are very high either, which probably makes him the worst player in the game by the end of it.

Keep Ropp because he becomes the best defender, and if you did sign Brother he becomes a great defender too. He doesn't have the highest AT stat, but his 99 speed means he can catch up with the fastest forwards (i.e. Datto and Nedus).

You have a fair few options for midfield. Linna is probably the best all-round choice as she can also shoot and tackle; but her endurance lets her down. Vuroja gets 99 PA but it takes him a while to get good. Mifurey gets surprisingly good; she starts off with a mesly 20 speed stat, but she does become one of the fastest players in the game, with some other great stats mixed in for good measure. Alternatively though I prefer to use Kulukan; she keeps her high AT stat and also gains a really high pass stat, making sure my opponents rarely get through the midfield.

As for forwards, I signed Argai Ronso as for a while he has by far the highest SH in the game, but you might not like him as his speed lets him down a little. Larbeight is definitely a recommendation though as he's probably the best forward overall if you look at SH and EN. I still wouldn't sign Keepa for that position because despite the 99 SH he has very few techs and low EN.