I would go for 2 actually - The great Gazza Kasparov and somewhat surprising but completely unbiased, Vishy Anand. Not only did they play some barnstormers with each other but in their prime, were untouchable in faster time controls.
Best Blitz player of all time

Capablanca gets my vote.
Alekhine: "His real, incomparable gifts first began to make themselves known at the time of St. Petersburg, 1914, when I too came to know him personally. Neither before nor afterwards have I seen – and I cannot imagine as well – such a flabbergasting quickness of chess comprehension as that possessed by the Capablanca of that epoch. Enough to say that he gave all the St. Petersburg masters the odds of 5–1 in quick games – and won! "
Fine: "I reflected on the fact that I could already beat Alekhine at quick chess while Capablanca, the few times I had played him, beat me mercilessly."
Thanks Quasimorphy for posting this. Capablanca had no rival at his epoch a true genius is reflected in rapid chess where "natural" moves take over your fingers faster than your thoughts

A story about Bobby Fischer's power in blitz was recounted on my blog... http://www.thechessdrum.net/blog/2012/03/16/bobbys-blitz-chess/

--edit - wrong thread --
But Bobby was a beast at blitz. You'd have to put Carlsen and Naka in the mix now too. Fischer and Tal have to be among top 4 all time.

Not sure about the best OTB blitz player, but the best internet blitz player was definitely Mikhail Tal:
https://www.chess.com/forum/view/chess-players/is-mikhail-tal-the-greatest-internet-blitz-player-of-all-time
First of all Botvinnik didn't calculate at all. He was completely a feel player. He would only calculate to make sure his strategic ideas didn't fail on the spot
fischer was a fast thinker. One of the highest geniuses to ever play in the game. He proved he was a monster blitz player
his scores against Spassky were only cited above to point out that IF YOU ONLY TAKE INTO ACCOUNT a current "score or rating" you're not getting the full picture.
Fischer's moves were compared by computer analysis on Chessmetrics and it has shown that he blundered the least and was arguably the most solid player of all time, (when you look at his final ten years of play anyway...)
i always thought Kasparov was the strongest, but it turns out that the beast he truly is, had a higher blunder rate than quite a few 20th century grandmasters. None of these results include the current crop of outstanding young grandmasters.