I've heard the Red and Blue chair is pretty comfortable considering how it looks. Years ago I worked up plans for a child-sized version of the Red and Blue chair for a friend who built it for her nephew. He seemed to love it. Of course children can sit on a pile of tin cans and broken bottles and be comfortable.
Jim, I like all sorts of different furniture styles including Mid-Century Modern. As I said, I'm considering the crate chair because it would be very quick to build and it would be fairly inexpensive. I haven't settled on it yet and I'm going to wait until it gets a little warmer and the DIY stores start stocking replacement patio furniture cushions to see what I can get easily. If I add cushions, most of the chair won't be visible anyway. The crate chair just give me an easy place to start. It'll be simple to modify the design to a two seater as well.
This is my sketch of it with cushions.