da Vinci's work was outstanding but to say he was the greatest is not necessarily true. I would hate to be the one to judge the great artists of the past. I feel that one cannot compare one the another in this field. All of these artists gave a lifetime of enjoyment where their art is concerned.
Though Da Vinci was not really an artist in the purest sense of the word, his marvels in engineering and invention should not go beyond recognition. Though he was perhaps not the most emotional of artists, the technical mastery of his works, such as, of course, the Mona Lisa, are unmatched anywhere else.
Da Vinci is a very accomplished artist. He has inspired and influenced a lot of artists but he is not the best. There are several artists that are better than him and have made better work. If you ask someone to name some of his art, they would probably only be able to name a few.
I think this could be one of the most highly debated questions out there. Da Vinci proved his talent with many different pieces, but I think if you ask some people there are some who will tell you Picasso, there are some who will tell you Van Goh, some will tell you Rembrant. There are many answers to this question.