Muir Woods has the most and biggest trees. However, as others have said, it's very crowded and you need to take a shuttle, etc. Lots of headaches just to get there.
If you want to see a very nice (but smaller) old-growth grove, try Heritage Grove in La Honda. You will probably be the only ones there. You can go there on the way to Laguna Seca. And plan on lunch at Duarte's in Pescadero.
Here's a link to a nice hike.
https://www.alltrails.com/trail/us/california/heritage-grove-loop-trail