You should always dress more formal than the interviewers to show that you really care about this opportunity. Especially if it's your first job. I would still go with black or navy suit with light color blouse. All the candidates we had last summer dressed this seriously. For brand, there are AT, Talbots, Alfani, Tahari ...... I feel that the brand itself is not important, as long as it is good quality, nice fit and you feel confident, beautiful and professional in it. This is the time to spend money.