We use the ones that have the metal uprights with bent plywood for the back. They are stiff enough to lean against and they pull flat when portaging. No backrest helps all that much while paddling, but they are great when fishing or resting.
We just tried out our new Crazy Creek Canoe Chair II's on our last trip. They are very comfortable, highly adjustable, lightweight, and fairly inexpensive. They have an adjustable strap with a quick disconnect latch for attaching it to the canoe seat. The tension on the backrest is also very easily adjustable. They are really great for giving your back a rest and while fishing in the canoe for long periods. I like that they have a Velcro strap to fold them down during portaging. You can also take them off of the canoe and use them as camp chairs too. I looked at a few other brands too, but chose Crazy Creek because they were lighter and cheaper and I knew that they made a quality product.
I really like the Crazy creek, but the design seems totally backwards to me. They should fold the other way. Also, it'd be nice to put a mesh bag on the front seat part that would hand down. Some cheaper chairs had this feature. While the chairs were junk, the pouch was great.
I have a crazy creek and tend to only use it when fishing. It maybe only in my head but I don't like sitting higher because of the seat when paddling. Nice thing about crazy creek seats is that they are comfortable on sunset rocks.
My crazy creek chair blew out a couple of weeks ago on a solo trip. I might have to try thrifty outfitters and see if they can sew it back together. I really missed the back support after it blew out. My solo yoke doesn't fit with my crazy creek chair installed so I had to disconnect the chair at every portage.