Virtually everyone will poo-poo these suggestions, but as a practical gay who gets shit done, I'm accustomed to it:
San Francisco Marriott Marquis (the one at 780 Mission Street): No, it is not super-posh, but yes the staff is great; it is near MUNI, BART, and SoMa parking garages; Marriott is very supportive of the LGBTQ community (scored 100% on HRC's Corporate Equality Index); and your SPG status should be good there now that Marriott owns Starwood. It is also a big hotel, so your clients' privacy and anonymity is pretty well assured
Hilton Union Square: BIG hotel that also has a Starbucks and a decent restaurant and bar. The rooms are OK and it is close to MUNI and BART. Parking is a bitch.
Hilton Financial District: I like this hotel, but the elevators are a pain in the ass, the streets nearby are all torn up, and there's not a whole lot of "there" there.