I'm doing One Winged Angel by Nobuo Uematso, and I choose it because I feel like it shows off a high level of skill without being too difficult for me to play well. It also features both fast and slow tempos, creating a nice variety and letting me demonstrate my own stylistic interpretation.
Before I dropped music I did Overture 1928 by Dream Theater as my core performance (on drums), because it incorporates a wide variety of time signatures yet was still fairly easy to play. Plus it's a good length too