My viewpoint is the complete opposite of the OP. I cannot stand SPG simply because too many of their Sheraton properties seem like they need a serious service upgrade, even after the big $2 billion investment in Sheraton in the recent few years by SPG and its hotel property owners.
I have had 4 stays with Sheraton over the years. Two of them were paid by United/Continental, and two were out of my own pocket (one paid and one award). None of them impressed me. The first one was in November 2000 when I was in college. I got stuck at EWR while flying CO due to ATC. After wearing out the CO employee [I was a clueless traveler but decided that it was either a hotel room or going to jail, and I wasn't going to jail without putting in a struggle], I ended up getting a room and meal voucher. I went to the Sheraton EWR and checked in after midnight. I got a smoking room, and the hotel looked like it was still set up for the '80s. The place was a dump, and it made a bad impression on me. The cheeseburger at the bar was overcooked, but I was tired and had a early morning flight.
My second stay came courtesy of UA after having a misconnect at IAD in December 2011. I ended up at the Sheraton Reston/Herndon. This property seemed a lot nicer than the Sheraton EWR until I got to my room and noticed green oxidation/rust on the bathroom door knob. The breakfast buffet was quite poor (no omelette or eggs made to order and a lot less fresh fruit than what Hyatt or Marriott would have). It was only somewhat better than the one offered by the Lansdowne Resort in Leesburg, VA (the prior hotel UA put me up at for a previous misconnect at IAD; they probably didn't do that again since I ended up with a late departure and the hotel had UA pay for a private car for me to IAD).
I was annoyed by the incorrect time for a clock in the hotel lobby, and the hotel employee who insisted that the shuttle was on time. The only good thing from that stay was that I signed up for SPG and got a free breakfast, after the front desk guy insisted that UA doesn't pay their food vouchers. I don't know if he was telling the truth, although I have noticed that the McDonald's in Terminal 7 at LAX has a paper sign stating that CO food vouchers are not accepted at that location. That is a corporate MCD location.
After those two stays, I should have avoided Sheraton, but I got a promo offer from SPG where one stay would get a free night's certificate at a category 1-5 property. I had an award trip with an overnight layover in NRT, and Marriott is somewhat lacking in affordable properties (a RC seemed like overkill and I wasn't going to spend 30k points on a CY).
I decided to stay one night at the Sheraton across the street from the Hyatt Dulles. I got a $55 rate for a club room over Labor Day weekend. The club was closed, but I got breakfast and internet with my rate. The service in the restaurant was quite lacking. How did I end up with a waiter who did not ask me for any drink preferences? The service was disappointing along with the food. Sheraton properties don't have good breakfast buffets. The fruit is lacking, and the inability to order eggs with a hot buffet seems cheap. Frankly, the food was not much better than the Hyatt Place next door, which is owned by the same hotel company that owns this Sheraton. I could not believe how much worse the service was at the Sheraton compared to the Hyatt Place. That experience told me that Hyatt has tighter controls over their franchisees than Sheraton.
The room at this Sheraton was small, and they had the heating/cooling unit right by the window of the room. It wasn't much different than the Hyatt Place in that regard, except that they used a desk and a faux wood cover to hide the unit. They have a laundry room, but I wasn't told this at check in.
I ended up at the Sheraton Miyako in Tokyo last month for my most recent Sheraton stay to use the award certificate. They have free internet for all guests. I found the property to be somewhat outdated since there were no TV channels in English or any language but Japanese. There were no business channels, and the room's furnishings looked out of date by at least 10 years. The breakfast buffet at this property was another disappointment. It was better than stateside Sheraton properties, but it was quite poor compared to food and service standards in Asia. I was asked for what type of tea I wanted to drink, and they never brought any hot water or tea. The food was okay, although I expected more hot items.