I just finished 3 back-to-back-to-back trips to SF. During the trip I stayed in 10 different hotels, including every full-service Marriott property except for Fisherman's Wharf. I am going to hopefully write a review of each property, but to know what is best for you, I think perhaps more information is useful about your trip.
Clearly you are going on a getaway and have platinum status, but are you only interested in full-service properties? What matters to you most on a stay? Are you going to be touring any specific area most? How do you feel about walking? How do you feel about homeless people nearby? Are you looking for a cultural experience?
Another one to consider is the JW. We'd a fantastic trip there and the staff were among the best we've ever seen at a Marriott! Called to check something out with front desk staff 4 days after we'd checked in and the staff knew our names without having to say what room we were in first!
We love the Marriott Fisherman's Wharf as it is in a great location for things we enjoy like Chinatown, North Beach, easy access to the Golden Gate Bridge and points in Sonoma/Napa, quick ferry boat ride to Tiburon and Sausalito as well as the must take Alcatraz tour boats. The hotel does not have a CL and parking like most joints in SFO is around $55/night, but we always get a great room with a tiny balcony (there is about four of them) and a very easy walk to the great dining in North Beach/Chinatown/Ghiradelli Square and even the Wharf.
The JW in Union Square has a CL that's open 24 hours. Breakfast is substantial and the evening snack is dinner worthy- usually. The location is great for getting to Market street and the streetcar, Chinatown via walking or the 30 bus and you're in the midst of many good restaurants in Union Square. Depending upon what you enjoy as a tourist and how long you're in SF for...I would choose the JW. Now, if you've never been to SF and you're interested in the many tourist spots near Fisherman's wharf the Marriott there is nice....but again no CL. Parking is probably a little cheaper. One note about the Union Sqaure location is the streetcar (F) on Market can take you right to the Ferry building which is at the Southern end of the Embarcadero or on down to the Tourist centric Fisherman's wharf area, or you can walk between the two....believe me you'll appreciate the flatness of the Embarcadero. SF is actually very small geographically so even if you don't stay right in Fisherman's wharf- you'll have easy access from about anywhere and there is plenty more to SF than Fisherman's Wharf. If you pick the JW- higher floors are quieter and the elevators are speedy. Others have compared the FS Union Square to the JW on this board. I have not stayed in the FS Union Square. Enjoy your visit.