Premed classes will be very competitive and academically demanding at any of a wide range of universities (both daughters had majors that overlapped with premed requirements and so I have heard multiple stories). I would be surprised if there is all that much difference in terms of which of these two very good universities would be academically more demanding. You will need to work very hard and make a strong effort to stay ahead in your class work at either of them.
If it were me I would be inclined to agree with @bluebayou, stay in-state, and save my $$$$ for medical school.
Since you are in state, you probably already know that Seattle crime is through the roof and getting worse apparently. I saw that a pregnant woman was shot and killed today downtown (not too far from UW). She and her husband were sitting in their car at an intersection. You may want a change of pace or scenery. On the other hand, Seattle might need more Drs especially ER.
UCSD is no less competitive for premed than UW. There is no reputational or med-school-admissions-related reason to pay double for UCSD over UW. If you have other reasons to prefer UCSD over UW, or La Jolla over Seattle’s University District, and your family has the means to pay the difference for those reasons, then that’s a conversation you can have. But you wouldn’t be buying any meaningful advantage as a premed by paying more for UCSD. As a WA resident, you’ll have an advantage when applying to UW’s med school either way; and attending UCSD won’t confer an advantage at CA schools or anywhere else.
You’d get a strong education at either school, and the competitiveness for grades, etc. is probably about the same. I personally wouldn’t consider passing up the UW offer unless there were significant issues in terms of major/program (i.e. admitted to desired major at one school but not the other, or something like that) but you didn’t mention wanting to do CS or other difficult-to-enter major so I suspect there’s no such issue. As others have said, save the $ for med school and enjoy UW!