Staying just about anywhere Downtown is good. The Sheraton, and Comfort Inn are walking distance to the 16th Street Mall. From there you can take the Mall Shuttle to where ever. Pretty much all the action is going to be on the Mall or a block or two off of it. The Hilton and Westin work too of course.
You might just want to look here.
Plenty to do, everyone will have an opinion. There really isn't a wrong choice.