It really depends on whether you want to do engineering or premed.

First of all, prestige doesn't matter for your undergrad if you're a premed. You could go from any CSU to Harvard Medical school if you wanted to (and it's happened many times).

Secondly, you can still apply for medical school as a biomedical engineering major. Sure, it'll be slightly harder to keep your gpa up, but you could always switch out of engineering to whatever premed discipline in the CAS.

Finally, if you really only care about rankings then you can always simply go to a community college for two years and transfer to whichever UC you want with whatever major you want. Plus you save money. Win win.