Struggling with what to wear? Formal business attire is almost always preferred for an interview. We all know we make a better impression when we're cleaned up and looking good, so why not take the extra time and look great.
Regardless of whether employees wear formal attire at the prospective workplace, you should dress to impress and show respect to your employer. It's more likely that you'll be sneered at for under dressing, not overdressing.
The other benefit to more formal business attire is your own self confidence. You will feel more professional, smarter and more self assured if you look professional.