Tal did himself in with his extremely poor health regimen. A brilliant mind gone to waste by its own doings.
Tal was WCC for less than a year, wasn't he?
Then he had some good streaks ion the 70's, I know.
But I really gotta go with Capa on this one. He was just born to be champion.
I've got two books (well actually I've got loads of books) 'The life and games of Mikhail Tal' and 'Capablanca Move by Move', they are great books very interesting and are full of great games illustrating the brilliance of each player. I don't know which was best and I'm not sure it really matters. The world of chess should just be very very pleased that these two men graced the game with their own unique genius.
In terms of chess writing and journalism, Tal wins easily. His books are classics of wit, insight and gentle self-deprecation. He makes the magical appear to be ordinary and within the reach of anyone. If someone finds a hole in his analysis, he doesn't get defensive, he admits it's not the best move, explains why he played at the time, then says what he'd do differently next time.
I am not sure that Capablanca ever admitted to making a mistake in a game he won!
You can never know, they never played each other.
Capablanca was callede "The Chess Machine" for no reason, and he was said to be the most naturally talented world champion. Unlike others who extensively prepare, he once admitted that before his first grand tournament(where he beat Nimzowitch) he had never opened an opening book yet he destroys everyone. Though chess I think is most interesting when complex positions arise, where Tal is a master of.
I don't quite know how to choose one over the other, but I will say that Tal succeeded in an era where chess was more professional and the road to the World Championship was much more difficult. In Capablanca's day it was "Pay to Play."
Also, don't compare them by the length of their reigns: Capablanca won one World Championship match and lost his first title defense, which was six years later. Tal also won one World Championship match and lost his first title defense, which happened to be the following year.
Capablanca is underrated for his tactical play, and Tal is underrated for his technical play. They mainly differed in their approach to complications: Tal sought them while Capablanca avoided them.
On a list of all-time greats I would rank Capablanca higher because he had a more dominant career, though Tal's dominance between 1957-1960 was as dominant a period as has ever been seen in chess history--I think more dominant even than Fischer's 1970-72.