My seat of choice is the BAR seat from Four Rivers Layout Blinds. It is sturdy with four different positions, waterproof and light. It keeps my legs warm and dry when sitting in the snow. It is around $90 shipped though.
On flat ground I like the one on the left , cheap, light, easy to carry, old knee friendly and I can see over the grass. For country where you can get some elevation either one of the two on the right, the center one will slide on snow as the legs are like sled runners, the right one will keep your butt warm and dry on snow.