<p>The standard advice is probably the best, to play the piece at the highest level you can where you are playing it in a polished fashion,because how you play it. I suspect you will get higher marks for playing the Sibelius Concerto at a high level over playing the Bruch at a high level, but if you had to choose between a polished Bruch and a less the polished Sibelius, Bruch would be the way to go.</p>
<p>The violin programs I am aware of require a bach solo partita or sonata as part of the audition repertoire and there is a reason for that. They were written to stretch the capability of the violin, and being solo, there is nowhere to hide, and you add to that that Bach is basically creating polyphony on a single instrument, and it is easy to see why they would want it. As GH said, what is fun about Bach on the violin is the artistic side is difficult, because no one really knows ‘how it was meant to be played’, Aaron Rosand of Curtis made a good point in an interview, he said that it is kind of idiotic to talk about playing Bach authentically, when we don’t know how it was played (no recordings in the 18th century), but more importantly, unless you are auditioning on a Baroque violin playing with a Baroque bow, playing on a modern instrument with a modern bow automatically makes it very different… </p>
<p>Bach is chosen for another reason, it is because musically it is very, very different then classical and romantic pieces, and they are trying to see if the student has learned to differentiate between playing Bach (or another Baroque piece) versus playing a classical piece versus a romantic one, it is amazing how many kids who are otherwise incredibly high level players have gotten through to that level without understanding the differences.</p>
<p>Mozart is an interesting one, it points out that difficulty is not everything (there is a reason why programs ask for Mozart). Mozart’s violin concertos are technically not as difficult as the romantic warhorses like the Sibelius, Tchaikovsky and Mendelsohn and their ilk, but Mozart has the distinction of being relatively easy to play technically, but is also very difficult to play well, in a way that is interesting, and audition panels are looking at that, to see especially if they are playing Mozart in a style appropriate to the classical era. </p>
<p>While playing technically flawlessly is a major goal, they are looking at musical interpretation and style, which is another reason to play a piece you feel comfortable with/is polished, that if you are struggling to hit the notes, play with solid intonation, you are likely to lose out on the musical/stylistic side.</p>