I played bass for all four of my HSC performances just recently, don't know what I got, obviously, but I played the same for the trials.
I played and got:
*'Spain' by Chick Corea and got 19/20 - with a drummer and pianist
*'Rhythm-a-ning' by Thelonius Monk - 18/20 - Same, had drummer and pianist
*'Blackbird' by The Beatles - 18/20 - I played the melody of the guitar and had a singer, sounded ace. Beautiful harmonies.
*'Steal My Kisses' - Ben Harper - 17/20 - had pianist playing what the guitar normally plays and drums. I didn't go as well cos it was quite repetitive, but the solo was my time to shine.
My advice is to get people who KNOW their stuff. Professional musos, luckily I had my dad whose a prof. jazz drummer and one of his muso mates, cos if you fuck up, they can cover it.
Jazz is always good. With those two first songs I went really well (they're jazz btw). You can muck around with jazz, so it suits you and you get really comfortable with them - you do really well with jazz pieces. And it really shows your technical skills, which is what they're looking for. It also helps you take control of the performance, and that's another thing they want. It allows for communication between the ensemble.
And also, with my marks, I had a terrible day the day of the trial, my marks reflect that. My teachers were listening on the other side of the door during my HSC performance and said they were sure of all 19s and 20s.
I can send you sheet music of the first three pieces I mentioned if you want.