There is no way you can ever decide on a "greatest" passenger plane. You would have to compare planes from different eras, each of which had to make best use of the available technology. Even with relatively modern passenger planes how can you sensibly compare a 777 with the best business jets?
Different planes for different jobs.
On looks terms Super VC10 and Concorde remain best in my view, closely followed by Caravelle and Comet. A DC3 also qualifies as a plane which "looks right".
If you mean the best in terms of safety, then the Handley Page HP 42 has arguably about the best safety record statiscally, which is pretty astonishing when you consider the available materials and technology of the time.