Yosimite or Muir Woods

Seriously, to me it's a tie between the two.

Yosemite is much more famous but they are both great in their own ways.

Happy trails,

Lake Tahoe is a 3 hour drive

I would say Yosemite hands down but it really depends on how much time you have. It's three hours away and to really enjoy it, you need to strap on some hiking boots and hit the trails. If you only have "a couple of days" you might try north of SF and hit Muir Woods, Stinson beach, and drive north to Point Reyes and Sonoma if you want some wine. I live in Marin and wake up everyday in awe of how beautiful it is here.

You should go to Baker Beach in San Fran

UPT. I am actually talking about the whole area north oh SF not just Muir Woods.

This is Baker Beach

It is clothing optional beach in San Francisco, you can figure out what you will mostly see there.

The whole Marin Headlands is a cool area. Besides visiting the Trees of Endor and the beach, drive up to Mount Tamalpais. It is the tallest peak in the Marin hills. It is very scenic and even better if you time it when the marine layer flows into the bay.

I've been to both. While Muir Woods is nice, it can be seen easily in a few hours. Yosemite is by far and away the better choice. Muir Woods is famous for the tall redwoods. You can see giant sequoias in Yosemite. IMO, a sequoia looks more impressive than a redwood. Plus, the sequoias are just an appetizer of what Yosemite offers. To me, the view from Inspiration point of the valley is the most beautiful overlooks in the world. Then there's half dome, Glacier Point, Nevada and Vernal Falls, Yosemite Falls, Hetch Hetchy, Taft Point, Sentinal Dome, three separate sequoia groves, plus the high country. You cannot see all of Yosemite in one day. You can hit the highlights, but there is just so much there.