Zion in early November is great... though sadly it seems like the post-peak period starts later every year.
All but a couple of my Yosemite trips over the years (and there have been many) have been in winter. It's so beautiful and there just aren't that many people.
I take it back... we did Zion in late October a few years ago and it was awesome. There were crowds but nothing too bad. We did the narrows and I wore a puffer and running shorts & shoes. Perfect weather.
Jan/Feb are the best in Zion because the shuttles aren’t running and you can drive the scenic loop in your own vehicle. We were there for four days in February right after a snowstorm and the whole park was covered in a fresh layer of snow. So beautiful.