I've only stayed in three hotels in Frankfurt:
Alexander am Zoo: Pretty dull, but clean, reasonably comfortable and quiet. It's a standard business box: you get a room with a bed, a wardrobe and a bathroom. It's within staggering distance of the Merianplatz end of the Bergerstr, so it's convenient if you're going to be partying up that way.
NH Frankfurt City: To be honest, I remember nothing about my room. There can't have been anything wrong with it, but it wasn't particularly memorable either. I do remember sharing the breakfast buffet with two (small) coach-loads of tourists: one Spanish and one Japanese. Centrally located.
Steigenberger Metropolitan: The
Frankfurter Hof is the Steingenberger Group's flagship hotel in Ffm. In comparison, the Metropolitan gets practically no attention, maybe because it's a harder sell when you have junkies shooting up two doors down from it, but once inside, it's very comfortable: good-sized rooms, lots of little extras, receptionists that actually smile at you. They even stock Henriot champagne (a personal favourite). A mere stone's throw from
Hbf, the red-light district, and the junkies.
I couldn't recommend
The Pure: a colleague stayed there and complained of snow-blindness. It's a little white apparently. Everywhere.