Rent has a variety of songs, but many of them can be characterized as:
- strong beat
- emotionally powerful
- forcefull
While singing a song from rent may be reasonable, I would personally look around for music that has similar characteristics that I can sing exceptionally well. You want to show off your talent. Further, to get that powerful emotion, you should pick a song that already moves you. It will be helpful if it's a song that makes you want to move and take action (even if it's a song about how you are stuck or can't take action). You probably don't need to dance during the singing portion of the audition, but they will be looking for people that appear to want to dance while they're singing, even if they're standing in one place.
So.
Find that one piece of music, sing through the whole thing, select the 32 bars of it that you sing the best, and practice, practice, practice. Deviating from the score significantly might be helpful, or might shoot you in the foot - it depends on the director and producer, but do what you love, and that should shine through your performance.
Also, note that I have absolutely no experience in this field and am probably way off base, but it's what I'd do, and obviously since I'm perfect you should try to emulate me whenever possible.
Plus I like rent, so I want to see you do it and be successful.