I have now rented motorcycles from MotoQuest's San Francisco base twice. Both times they've provided me with BMW R1200GS's - in excellent condition and ready to tour. The bikes come equipped with hard (and most importantly, waterproof!) side cases that can hold quite a bit of gear. I travel with light photo and video equipment, and went through some tough weather - no issues.
What I like about MotoQuest is their attitude. They are very accomodating, and went out of their way to reposition a motorcycle to San Francisco from their Long Beach headquarters so I could make my recent trip. The bike was delivered with the fuel topped up, tires, oil and everything checked out. I also got some helpful routing advice from their rental team, who seem to have an excellent knowledge of West Coast touring options. I'm and East Coaster who loves riding California. There's such a great variety of roads...mountain, coastal, canyons, valleys, etc. and the scenery is endlessly spectacular.
Go ride there, and if you need a motorcycle, call the gang at Motoquest.