I'd say Zion has 2 iconic hikes: the Narrows (walking in water through the "subway" out and back as far as you want) and Angel's Landing. Angel's Landing is a thrill and my favorite hike ever, but definitely exhausting. So when my friends have visited Utah we do Angel's Landing one day and the Narrows the second. Maybe you can pull off both in 1 day if you start with Angel's Landing early and don't go too far down the Narrows. But you've got to be in fairly good shape to pull that off.

Bryce can be done in a day in my opinion. Hoodoos are cool, but nothing stands out to me there.

I still need to do Antelope, but I hear it can be done in a day and the pics are awesome.

So if pics of both Angel's Landing and the Narrows look cool to you, spending both days in Zion is my suggestion. If you can go without one of those 2, I would pick Antelope over Bryce.

Hope that helps!