It's so hard to pick just one, and I think it depends on what you're looking for. But if forced I would choose:
LACC N for the pure golf, it's world class and combines fun and challenge better than 99.9% of courses in the world.
Riviera for my future retired self, incredible setting and great architecture at its bones. Sure I wouldn't be able to play run-up shots, but I grew up playing kikuyu and the teed up fairway lies more than make up for it.
Rustic Canyon for my college / post-grad rounds on a budget, a time where I'm able to study the architecture and repeat plays for insanely cheap in a reasonable drive time from the city.
Wilshire for the membership and vibe, because the people and staff are crazy friendly and it's a sporty, social track that plays wayyyyy better than a course in the middle of a city on a property that size should. It's the essence of classic LA golf.
And for a life that isn't mine, Bel Air (pre-Fazio or post-Doak) for a getaway from my uber successful acting career where I can golf with my buddies, agent, and fellow celebrities and get the same 5-star treatment I get in the rest of my life.
Sidenote: LA has more solid courses than it gets credit for, but way off my radar was Knollwood which I played on a whim yesterday. Would love to see a facelift there (and Santa Anita, and Rancho, and Rec Park, and...) as it's one of many could-be great courses that could make up for how little quality public golf currently exists per capita.