Ahhhh the cello days, nothing but fond memories.
The best thing you can play during an audition is something you know very well, and that is something YOU enjoy. It doesn't have to be the most difficult piece you know, but it needs to be a solid performance. That's what I'd expect from someone auditioning for our group I play with (but I don't call the shots). But more importantly would be your ability to adapt to our songs and the way we play them, and last but not least - the proper attitude. Attitude will make and/or break your chances.