I lived in Antioch, CA. for three years from 2002-2005, which borders both Brentwood and Oakley. In my opinion, Brentwood has better infrastructure, such as brand new schools and housing developments, yet still surrounded by the rural agriculture. We always went to Brentwood for the fabulous farm stands and u-pick farms. Brentwood is more visually appealing as well, to me personally. I would try to prioritize what your biggest needs are for your future home. Is it schools, a reasonable commute, access to transportation? You may also want to check the crime rates for each area to help you make your decision. Have you been to both locations?
Good luck with your search. Feel free to email me with any additional questions you might have regarding that general area. I am a Home Stager, not a realtor, so can only provide you information based upon my personal experience.