If you're wedded to Marriott, there's one just off the 5, close to both La Jolla and Del Mar: http://www.marriott.com/hotels/travel/sandm-san-diego-marriott-del-mar/ That said, it's not within walking distance of anything you might want to see/do.
Might be fun to check out the inexpensive (by San Diego standards) places down on Pacific Beach -- not fancy, but great
location. We used to live in San Diego (not far from the Marriott I mention above), and when we moved to D.C. and my husband would go back to S.D. on business, he'd pick one of the Pacific Beach places to stay.
Post Edited (Bluepencil) : 12/31/2015 1:44:52 PM (GMT-7)