If You Must Stay Downtown
We have stayed here a few times. The place is huge and impersonal, but the room is neat, clean and comfortable. It is located in the downtown area, across the street from the subway (the Bart) and only one block from the Powell Street cable car turn around. 
The upside to staying here is you are in the middle of great shopping if that is your thing. Also, this place will have some dates that are tough to fill. So they will offer some really great sales with prices chopped drastically. But those sales bookings must be done through the 800 number of their own company. I have seen this place go as low as $75per night, but it can also go more than $200 per night for a regular king. 
The downside to staying in this area is of course no free internet unless you join their rewards club. Also at night the neighborhood is not the best for going out and walking around. There are a lot of people who will approach asking for handouts. Many of the restaurants are closed and it can quickly appear to be a ghost town of sorts. Some people will find it frightening at night. 
Also parking can be tough. The Valet service at this hotel can get hectic and the prices are $40 or more plus tip. Plus there is very little street parking in this area. 
If you need cheaper parking in San Fran do consider this. There are some $10 park all day lots around San Fancisco. I have seen them around china town and around Mission Street area, 6-8st. Those lots appeared to be safe. There are also similar lots on Jones street just a few blocks in from Market, but that area can be dicey. (Think a Seinfeld episode about the parking lot.)
But keep in mind, street parking in Sf is tough and there are more than 40 ways to get a parking ticket. For that long list go to the SF parking violoations website.
Many street meters are free overnight while others become tow-away zones. Read the signs carefully.