I can't think of a single IC that I dislike except for the IC Mark Hopkins in San Francisco. Although the hotel holds a great deal of sentimental value (my grandparents celebrated their 50th Anniversary here) it doesn't compensate for the antiquated rooms and paper thin doors that amplify hallway noise.
My personal favs where I was always been upgraded when I had Ambassador status:
- IC New Orleans
- IC Athens
- IC Madrid
- IC Lisbon
- IC Prague
- IC Miami
I've also had good experiences at the IC Chicago but you have to avoid some rooms that are real dogs.