My birds' favorite box is a wicker cat bed that I attached to the wall. It's like a spherical basket with a 6 or 7 inch hole in it. I have traditional wooden boxes too, but that one's their favorite.
Chickens will nest in anything (as long as it is large enough)... so you can be creative and as artistic as you like... or not...
I have used, and my chickens have enjoyed..... a see though plastic tote screwed to the wall, cardboard boxes on the ground, crate on the wall, small bookshelf on it's side, wooden box under a poop shelf, the back corner of the poop shelf (not really bad, forces me to keep it clean), plastic buckets screwed to the wall....
Oh, and for awhile I had one hen that loved to jump into my hanging metal feeder, lay an egg on the feed... then hop back out.