I bought a fairly cheap one and have been more than happy with it. I don't know if I have the same problems as you guys do though. My knees and ankles start to hurt though if I do to much running or jostling.
Mine has always been fantastic and both I and my boyfriend (who is 6'1) use it. He uses it more than me and has lost about 30lb off of it.
Really go to a store and try them out. There are plenty of places that will let you hop on it and give it a go.
