Who is the best person to beat Magnus Carlsen?

Lasker's title defenses have a big asterisk next to them. He didn't play Rubinstein, Nimzo, or any of the other strongest players after WWI until he faced Capablanca. He tried to avoid playing Capa, too. 

For me, Kasparov is the greatest World Champion ever. He defended the title against Karpov, probably the second greatest WC ever, and then went on to defend it against Short and Anand before losing it 15 years after he first won the title. 

Karpov only defended the title against Korchnoi with the 1984-1985 match against Kasparov ending undecided. 

Botvinnik deserves a shout out for his brilliant play in the rematches. He's the only player to never win a World Championship defense, but to win every rematch. In many respects, he was like Muhammad Ali in boxing.

Carlsen has a ways to go before he's the greatest champion ever, but he's making good progress on the way. Tiger Woods may be a cautionary tale though. He was the greatest golfer for several years, but could not match Arnold Palmer's longevity.

Karjakin said in a recent interview that he was "a victim of too much respect" for Carlsen, and that's why he missed the drawing move in Game 10. I guess Anand too, who missed a winning move in their last WCC. They just never expected that Carlsen would play a weak move or miss something.

Someone who can beat Carlsen must also be someone who doesn't give a damn who Carlsen is. That person is the one who will beat Carlsen. 

Why are chess computers so strong? For one, they don't know and don't care who you are. Psychology has no effect on them.

Good post SmyslovFan

Of course, chess compuyers first needed to learn how to play chess. But today. in match play, chess computers will always win, no question. I quoted those examples where human weakness showed itself, in this case with Magnus and his challengers. Not so with computers. If you gave them even half a present, it's over - within a second.

You are such a Carlsen fan boy. He has won two matches and against an old man who is only a shell of his former self. He did NOT just win a match against Karjakin. The match was tied.

Kasparov played 8 world chess championship matches. One was aborted, one was lost, and one was tied. He won five.

All of Carlsen's matches have been so short they can't even be considered legitimate in comparison to past champions.

"An old man who is only a shell of his former self"

are you trying to disrespect anand

I think he's acknowledging that Anand was not the player, in 2013 or in 2014, that he was in 2006. Peak-level Anand would have been a significantly tougher challenge. 

Carlsen´s only weak points are the opening and emotions, so...

Criteria:

1) Has to be capable of winning candidates

2) Has to be able to tire magnus out with draws

3) Has to have very good opening prep

4) Has to be very good at rapid.

Karjakin met all 4 and still failed. Kramnik, perhaps?

I'll add that in the same interview Karjakin also spoke about his friendship with Carlsen. So I don't think he had the "killer instinct" against Magnus, while Carlsen seems to me more ruthless than Karjakin. (IOW Sergey looks to me a "softer" person than Magnus, and probably their friendship weighed more on Karjakin than on Carlsen - imo ofc)

Karjakin defended long endgames very well. That should have been the very first thing you listed. If someone can't defend endgames, there is no point in winning the candidates other than for a good pay check.

My money is on Justus Williams...someday that kid is gonna be WCC

Isn't he 18?

there was once a farmer who had a dog

I thought he was 16...where did you get 18 from?

Justus told me that someday he will be WCC.  2nd one from the USA

Fab or Giri

I reckon Carjacking will jack Magnus' championship if first to two wins up, draws not counted, is the decider. Magnus is undoubtedly the blitz champion of the world, but that is ALL that has been proven. Don't think that's what the challenger was playing for, do you? I'll tell you why. Draws will increase as the game is better understood. They should be ignored. But some principles applying to blitz play are very different. Such are also detrimental to non-time-deficient play, and vice versa. Saunton was defeated by an unknown who spent 5 hours per move, who in the process invented the Queen's Indian Defence. Staunton promptly introduced  time controls! When bamboozled by outlandish pieces, he standardised them. I wish he was playing Magnus. He might just help bring in Blitz with Fischer time controls, that disallow guillotine conditions, and outlaw increments that more than double the rate of endgame play (3 seconds minimum per 2 minutes clock!).

"I reckon Carjacking will jack Magnus' championship if first to two wins up, draws not counted, is the decider"

Because...? I think Karjakin's strategy from the start always was to try to hold and wait for Carlsen to get impatient as the number of games to decide it diminished. It happened for real first in game 8, when Carlsen avoided numerous draws to try to win and eventually lost. Then he equalised in the tenth game. I see no reason to assume that Karjakin would have won if it was first to go two up in classical chess that was the decider.

"Magnus is undoubtedly the blitz champion of the world, but that is ALL that has been proven"

Grischuk is the blitz champion, while no blitz games were played in the title match.

"Gaap" seems to be very good.