The two museums aren't the same day trip. The de Young holds the Fine Arts Museums' American and international collections plus rotating contemporary shows — check the website before you go because ticketed special exhibitions sit behind a separate paywall even on free days. The Legion runs stronger on European paintings and the Rodin sculpture garden outside, which is free to walk regardless. Both have cafes; the de Young's Café de Young is the better lunch stop if you're spending the morning in the park.

If you have two hours, pick one and commit. The de Young's permanent collection on the second floor — American art through the 20th century — can be done well in 90 minutes if you skip the decorative arts wing. Save the Legion for a separate trip when the weather clears enough to make the garden worth it.