What Kind of riding are you looking for? What are you going to study?
SDSU and UCSD are within 15 miles of each other and both are near great riding. Of course UCSD would be my pick cause it sits above Blacks Beach (epic surf). UC Irvine has good riding within a half hour or so, but you couldn't pay me to live there. UCLA is arguably the best school out of your pics, but the furthest from good riding do to traffic. However UCLA does have Santa Barbara 2 hours away, OC and SD to the south and MT. Wilson to the east.