Just spent three nights at the St Regis Grand and it was fabulous. The restaurant was excellent and reasonably priced. The rooms were quite luxurious. The location is great... one can walk from the the St Regis to the Westin in about five minutes, so as far as I am concerned, no difference.

Also spent two nights at the Westin Excelsior in Florence. Excellent property, no compaints, but nothing spectacular either. The Grand in Rome WAS spectacular!