If you had to rebuild your office shoe collection, where would you start? What would your top picks be?

Most of my office shoes - black mules, white mules, black (super cheap and uncomfortable Old Navy) loafers, green flats - are in need of my replacing ASAP due to wear and tear. I'm now in my mid 20s and bought most of these when I was broke straight out of college. I'm looking to replace them with some higher quality picks and am curious as to hear this sub's ideas, especially given the recent trends in office footwear (e.g., mules being super in and then seemingly over played, ballet flats back in, etc.)