You are right the rankings pertain to the graduate program, but it means there is a lot of activity and resources in the dept and that will greatly benefit the undergrad program and opportunities. I would pick UCLA. Your are not moving from the Bay Area. Your home base is there, you will return there summer or at least part of the summer and breaks. It is easy to get back and forth on the megabus or just carpooling for any weekend or break. You are not establishing a home in LA or getting a car, I presume. I just don’t see that you are moving. I don’t think my kid considered that she moved to Providence to go to school there so this is a strange concept to me. You are just getting the best education you can and immersing yourself in your school community wherever it happens to be. Once you start a career you can pick whatever you like to live presuming there are jobs. Are you very young transfer that two years is a long time to you?
I think the Computational Linguistics major is a huge bonus as you can be specific to that field in technical applications. But you have no wrong choices here.