Comparison:
Santa Barbara (Slightly cheaper):
$12,508 in-state
$35,386 out-of-state
Classes with fewer than 20 students: 45.0%
US News Ranking: 42 (Decent)
Student to faculty ratio: 17:1 (Decent)
Davis (Slightly more expensive):
$12,794 in-state
$35,672 out-of-state
Classes with fewer than 20 students: 36.1%
US News Ranking: 38 (Better)
Student to faculty ratio: 15:1 (Better)
Honestly I would go with Davis. A little more recognition there. Especially for Biology. Both of my parents are Biology professors and say the Davis program is really good. Only thing is at Santa Barbara you get smaller classes for less tuition (biggest bang for your buck). Another thing to keep in mind is that at UC - Davis Biology is one of the top five majors (for good reason). Personally I would pick UCD. But it's up to you. Also where would you rather live? Santa Barbara or Davis? I've been to Davis and liked it. Never been to SB.