Mercure--good value
I have only been to SD twice, but stayed here each time. Yes, rooms are small, but great location and good price. I have also visited the large Renaissance hotel and realized it could be almost anywhere in the world.
At the Mercure, you are in the heart of the action--I like it.
Yes, prepay on line for the best deal. I have not tried the "chica" angle, but I will succumb some day I am sure.