Having done Redwoods national park and Sequoia national park within a few days of each other early this summer, here’s my advice:

Redwoods contain a lot of California Redwoods (Sequoia sempervirens), and they are super impressive. But Sequoia contains a lot of Giant Sequoias (Sequoiadendron giganteum), and those just boggle the mind. It’s like being on another planet. I very highly recommend The Congress Trail, which starts at the largest tree in the world (by volume) and continues through multiple groves.

So do Sequoia second, or just Sequoia if you have to choose.