What an interesting thread!
It's hard to say which in my favourite camera, I think I would have to go for the Marconi MkVIII. It's a nice camera to work on and the build quality is very high and the auto line-up is quite impressive. As has been said the pictures can be a bit variable. A lot depends on the quality of the Plumbicons and the skill of the set up, Yes you had to set it up before the auto line up could do it's job. After 40 years it is still a reliable camera. Must turn it on again and blow the dust off.
Next favourite would be the EMI 203 IO camera from the early 1960s. This was the second IO camera that I got working, a nice slim camera and easy to repair. Transformers reliable, capacitors a bit dodgy after half a century. almost entirely valve construction. I have a full set of accessories for this camera.
http://www.tvcameramuseum.org/emi/203/203large1.htm show the camera with 4 lenses and a diascope in the 5th position. I also have the original valve SPG for it to operate on 405/525/625 lines.
It's getting harder now, I suppose the next in line is the Pye Mk7 IO camera. this is a late model (1966) solid state camera IO camera with a purpose designed zoom lens. The camera is in "as new" condition and the CCU is small and light (relatively). Here's a picture of the camera
http://www.tvcameramuseum.org/pye/mk7/pyemk7inf1.htm
On the subject of picture quality a lot depends on the tube, as well as the camera line up, amount of available light. it is important to compare like with like. the three cameras I have chosen span just a Decade (1960-1970) and in that time cameras went from valve IO (the EMI203) through solid state IO (the Pye Mk7) to the Marconi MkVIII (colour with auto line-up and integrated circuits). A real decade of progress. All three cameras are in the collection and are in working order.
regards
Brian
www.tvcameramuseum.org