Hands down - my favorite Marriott affiliated property in SF is the Stanford Court.
I travel extensively on business and spent a good portion of October / November in San Francisco. After trying several other properties, I happened upon this one and fell in love. This will be my first choice going forward when I need to be in San Francisco.
Check In The checkin experience was smooth and efficient. I had no issues. When we discovered that my Marriott number had not been included in the reservation, it was added and I was given an upgraded room.
Room Regular rooms are a little on the small side, however, are definitely adequate. The corner rooms they use for upgrades are great! Although hallways are a little worn, the rooms are newly redone and have a modern flair. Beds are comfy and bathrooms spotless.
Concierge Lounge While I was staying this fall, they opened their new concierge lounge. It's an excellent amenity. Breakfast options are the standard eggs, fruit, bread, pasties, hot / cold cereal, etc, but the service and staff make it so much fun! Views from the lounge are great, especially at sunset. Happy hour appetizers are very nice. There were 1-2 hot items, veges, cheeses, cold cuts, etc. I really enjoyed this lounge, and I've gotten to where they don't generally impress me much.
Location / Transport From it's location on Nob Hill, it's a quick cab or trolley ride down into the financial district. The hotel also has a complimentary car service they'll let you use if it's available. Beware of rooms on the lower floors on the California side of the building -- you'll hear quite a bit of trolley noise at all hours.
Atmosphere / Character What I like most, is the feeling. The property is small enough that people know you. They remember you and are very friendly. This very much feels like a little boutique hotel with the Marriott / Renaissance amenities.