Denver, CO:
Best: 1999 Broadway. Though it's neither the tallest nor most distinctive landmark on the Denver skyline, 1999 Broadway is, in my opinion, the most unique and architecturally interesting. It was built around (and on top of) an old and historic church, the Holy Ghost Catholic Church, so it looks almost like the two buildings are connected.
Worst: Brooks Tower. Sorry, is this Denver or the Bronx?