Based on MY experience, I would recommend Monterey for one night and either Cambria or Pismo Beach for the second.
Drive times: Monterey to Santa Barbara is close to a 5 1/2 hour drive WITHOUT stops. Since this stretch is the MOST scenic part of the coastline, you will want to take your time to enjoy the sights along the Big Sur coast. I would say the actual average drive time to include just a few well placed stops en route could be close to 10 hours, especially if you plan to include Hearst Castle into your itinerary.
I also tend to recommend NOT driving any further south than Pismo Beach because that drive along the Big Sur coast is quite tiring. You'll be on roadway that sits hundreds of feet above the Pacific Ocean with sheer drop offs in several places and LOTS of deep, tight hairpin turns. Your average speed will be 35-40 MPH along that 90 miles of coastline. By the time you roll by Pismo Beach, you'll feel beat up. I drive that route several times a year and I still feel beat up by the time I reach Pismo Beach.
Once off the elevated section of Highway, you would still have 3 more hours of non-stop driving ahead of you before rolling into Santa Barbara. And there's still a lot to see/do between there and San Luis Obispo: Elephant seal rookery, Hearst Castle, Cambria, Morro Bay/Rock.
But, as mentioned. it is your trip. You can proceed with it any way you want. If you want to limit your time on the scenic beauty of the coast for a more urban Santa Barbara, that's up to you.
Edited: 5:21 pm, February 13, 2013