S.R.
They are not super similar... Both are worth a visit in your lifetime.
Yosemite, there is nothing like it. A glacier cut through the valley and the various landscapes are just spectacular. It's forest, meadow, creeks, waterfalls, domes, cliffs, the works. The only downside is that California has barely had any rainfall this year, which I can imagine means not much snow in the Sierras. So I think Yosemite waterfalls will be nothing but a trickle, which is a little bit of a bummer. Don't let that deter you, Yosemite is amazing. There are tons of great hikes and you can definitely spend 3 days there doing some serious exploring and hiking. As someone mentioned there are giant sequoias in Yosemite, that you can walk through and there might be one you can drive through (or used to).
Sequoia is pretty much the big trees and the forest. There are some pretty amazing giant trees though, I think the biggest ones are bigger than any of the ones in Yosemite. The "General Sherman" tree in particular. There is also a Sequoia tree stump you can walk on that is the size of a dancefloor.
This isn't as close to the other two you are going to, but if you really want to see one of the most beautiful natural settings in California, you should consider the Coastal Redwoods. Particularly the Jedidiah Smith State Park along the Smith River. It's gorgeous, the height of the redwoods is mind-boggling, and along with Yosemite I feel it one of the places in our state everyone should see. Unfortunately it is at the very top of the state and most people coming to Ca don't consider going up that far.
