Self-correction: USC and Brown both rank #20 in USNews for CS:
The Sciences - Best Graduate Schools - Education - US News and World Report
(I'm sure you already knew that but I didn't.)
So, anyway, I would be leaning toward USC or Brown. (Accept both if you have to and then make your decision ASAP. I assume you are still waiting for admission from USC. So I would accept Brown, at least for any April 15th deadline, which is obviously today.)
USC offers the traditional MS option, which is attractive. OTOH, I would think a PhD admissions committee would favor Brown in some ways since USC seems to be known as a safety school for MS students. Then again, USC's tuition seems significantly less expensive and they are ranked the same for PhD CS (#20 in USNews).