My vote for ugliest would be that hideous thing across from the old Dade County courthouse on Flagler...the one with the blank concrete facade on the west side facing I-95 (don't know the name of the building).
That said, I couldn't help but notice your avatar. I don't know if you are aware of the band the "Eat" but they were absolutey the greatest punk band to come out of South Florida and influenced countless people in that scene...including myself. Eddie and Mike O'Brien, two of the founding members, remain friends today. Very cool to see that.