The Sheraton Mofarrej is one of the big five-star hotels in town. That being said, if you can afford to stay at a five-star hotel in Sao Paulo, I'd say stay at the Renaissance unless your company stipulates the Sheraton.
Certainly I have no quibbles with the service. The concierges and the desk clerks were all kind and helpful, consistently making me restaurant recommendations and reservations. The business center was well-equipped as well for all my needs. Even the bell hops were terrific, making sure I always left and arrived with a smile (even though I knew I was overpaying on their car service).
Room service was fine but overpriced, and the breakfast buffet was absurd -- who can eat US$25 worth of food at 8am? The lobby was dark, and the lobby bar was not condusive to mingling. You cannot sit at the bar, but rather must sit at a table and wait for waiter service. When travelling alone on business, it is very hard to meet other singlets this way. (The lobby bar is the single most important aspect of a hotel for me when I travel on business.)
During my stay, many of the guests were there for a corporte conference (which are normal for this hotel the desk clerk told me). Thus, it may be wise to reserve far in advance to avoid being booked out. The guests were perhaps half Americans and half Brazilians, with some Japanese, too.
My room was clean and comfortable, with a minibar and a desk with dataport. I had a view of the avenue and Trianon Park, which is right next to the hotel and a fine place for a walk (it is very shady and quiet). The hotel is in the Jardims area, which means you are near fantastic shopping and restaurants as well as a few cinemas. You can walk around this area at night, and by yourself during the day.