Well this thread has taken the awkward turn or two.
After having owned many kirbys (G6, 3 heritage 1 & 2s, Omega, tradition, 518, d80, heritage 1, Diamond Edition, Ultimate G, G3 etc) and several sanitairs (SC888, S677D, etc)
I have come to learn that with my carpet, a sanitaire always seems to get down deeper, and pull up more stuff than the kirbys could. Especially pet hair.
Now the kirby was no bad cleaner or anything. They do what they do, and are great at it. On many kinds of carpet, they can excel. But my carpet at home, its not quite at its best.