Hello, there, I graduated from UCSD in 2014 with Biochemistry and Cell Biology BS. If you're seeking a research program, you should definitely look into UC San Diego over UC Irvine. The reason is the following:
1) San Diego/La Jolla is the best pub for biotech/engineering/technology companies. You can find all these big companies such as Johnson&Johnson, Pfizer, Thermo Fischer, Northrop Grumman, Salk Institute, Inova, Beckman Coulter, within 15 miles radius from UC San Diego.
2) The transportation is much better, most of all included in your tuition (sort of free) if you're attending UC San Diego, you get a sticker each year which is on your student ID card This allows you to commute freely (bus, trams in downtown San Diego).
2) Community: Did you know that San Diego is considered one of the safest and most affluent city in the US? I mean it's not as good as UC Irvine (top 4). But, still, San Diego is one of the best places that I'd want to go back once I get my master program in Irvine.
UC Irvine:
1) New city/New Community: The community in irvine itself is very new. It is considered the safest city (among others).
2) Transportation: as long as you're within campus, you're good to go. But, finding a parking (even with your parking permit from campus) it would be harder for you to find a spot during weekdays. But, you won't necessarily need a car since everything is nearby! - groceries, libraries, places to hangout
3) Research wise: There's some couple companies beckman coulter, thermo fischer also branched out in Irvine. But, not as much as San Diego. But if you're considering to commute Irvine and LA Area, Irvine is way to go. LA doesn't have much job career for biology/life science major but since we have the engineering side of it, you can find other engineering firms/companies near LAX (which would be 40-1 hours commute from UC Irvine campus).
There's definitely both pros and cons of San Diego and Irvine, but I'd say San Diego because there's so many biotech companies and hospitals. best place for all scientists especially if you're studying/researching on BME