Go with the pants. During my interviews, probably 2/3 of the women wore pants. I found the PERFECT pants suit and wore it to every single interview. It looked great, felt great and WOULDN'T wrinkle (remember, you'll be doing alot of traveling)!!!! Do be conservative though. My suit was black with black pinstripes and I wore a beige silk blouse. You should also use minimal makeup and jewelry. And don't forget the MOST important thing...comfortable shoes! Most programs want to really show themselves off and insist that candidates take lengthy tours. 😱 Also, get a nice attache' for your things...don't carry a purse. 😀
Finally, you'll need to take along another nice (but more casual) outfit, as most programs like to wine and dine you the night before your interview. It's usually a group event with all the current residents and interviewees. It's a chance for you to ask questions in an informal environment and for them to make sure you're not a social *****. 😉