The default space wallpaper is by far my favorite. It's the right balance of not being too busy or too plain. Most wallpapers don't work well in iOS 7 because simpler wallpapers look good on the home screen (complicated wallpapers interfere with the icons), but simple wallpapers look too plain on the lock screen.
The space theme with the green aurora is nice but I don't like how it makes the dock a green block. The third ice theme one is pretty nice. All the other nature ones are so-so. I really like the gradients, especially the turquoise one. The three pattens that follow are absolutely horrible. The bright shapes are nice, but only for the lock screen. The 5C defaults are meh, I think Apple should have used the dynamic wallpapers for the 5C instead; they look nicer and would be a good way to show it off.
