Luckily for you fanboys, there exists a study which more or less tries to answer this:
«The question usually asked at this point by most people is: "Then, who is/was the best?" Well, as for simplest questions, there is no trivial answer. Distribution or Markovian methods do not provide rankings, they just provide a way to rank a pair of players. However, a simple (and partial) answer is provided in the following table, which is extracted from the article. Each cell is the percentage of the expected result of a game between the two corresponding players, taken in their best year(Carlsen: 2013, Kramnik: 1999, Fischer: 1971, Kasparov: 2001, Anand: 2008, Khalifman: 2010, Smyslov: 1983, Petrosian: 1962, Karpov: 1988, Kasimdzhanov: 2011, Botvinnik: 1945, Ponomariov: 2011, Lasker: 1907, Spassky: 1970, Topalov: 2008, Capablanca: 1928, Euwe: 1941, Tal: 1981, Alekhine: 1922, Steinitz: 1894.). The table is not symmetric as it is not the same thing to play first or to play second. The left column is more or less a ranking of the 20 World Chess Champions. However, to understand all the ins and outs of the method, you should read the complete article [0]. » [1]
And according to this article [2], Capablanca and Fisher are the most accurate players.
But the G.O.A.T. is obviously none other than Judit Polgár, get over it.
P.S.: (y)Our friends (?) at chess dot com give Morphy an ELO-rating of only 2409, btw [3].
[0]
www.alliot.fr/CHESS/draft-icga-39-1.pdf[1]
www.alliot.fr/CHESS/ficga.html.en[2]
www.scribd.com/doc/132380754/Chess-Player-Analysis-by-Rybka-3-14ply[3]
www.chess.com/article/view/who-was-the-best-world-chess-champion-in-history