Mechanical to be exact. With grants, both are roughly the same cost.
I would consider UCR for mechanical engineering over SDSU. UCR’s engineering college is relatively new and is ranked first in the nation for its small size. The student to faculty ratio is much smaller at UCR as well considering SDSU does have almost 10,000 more students. SDSU has a good mechanical engineering program and San Diego has much more to do than Riverside but you will receive a much better education at UCR for your major since UCR is above even UCSC for engineering. There are many clubs at UCR and the social scene isn’t dry as long as you put effort into it. I say UCR since you mostly should be going to college for an education.