Shanks! Whitebeard is only a shadow of his prime.
Shanks showed no fear who ever he was against with, in fact he pretty much does what ever he wants, and succeeded in everything he wanted to do. I believe being an ex crew of Gol D. Roger, he is the nearest to becoming the new PK, in fact he can pretty much get One Piece if he wants to, just that he doesn't. He's more interested in keeping the peace and the balance of the world. Red Hair Pirates are the Peace Corps in One Piece, making sure there is peace and balance. He only fights when it's necessary.
WB lost Ace, lost to the Marines and lost to BB, and he is dead, he died a loser.
If and when Whitebeard uses both hands, ambidexterously, Shanks has legs, but what's more important are what's above his shoulders, and Oda pretty much emphasized Shanks lost no battle power even with losing one arm.
If Squardo can drill a hole to Whitebeard, Shanks can do better. Heck I did not see WB stop Akainu's fist, only Shanks can do that, BB was not even afraid of the old man, but he waived the white flag to Shanks. Shanks, was even unscathed from his meet ups/skirmish with Kaido.
Whitebeard wasn't exactly shaking in his boots at the sight of the marines - In fact, Sengoku was the only guy who was terrified, and of whitebeard.
If your argument is 'he's highly ranked and was in Gol D. Roger's crew, so he's close to being pirate king', then can I please point out that the same criteria could be applied to Buggy or Silvers. As it stands, Shanks is one of the very strongest people we've seen, but Whitebeard - while almost dying, letting himself get wounded, being stabbed by someone you treated as a son - and were a good father to, if the vast number of crewspeople crying at his death was anything to go by. He was betrayed.
Gol D. Roger isn't around any more, he died too - in similar circumstances, in fact. Would you saying 'Whitebeard died so sucks' also mean that you think Gol D. Roger is pathetic and would lose easily to the likes of Shanks or Blackbeard?
Whitebeard has legs, too, first of all, and also what IS important about Shanks? He blocked one of Akainu's punches, and knocked out a lot of weak pirates. Akainu having already been kerbstomped by Whitebeard. Before Whitebeard beat up Blackbeard. Oh, and
after WB had let himself get
stabbed, repeatedly, frozen, hit with a magma attack and shot by lasers. Whitebeard wasn't deliberately taking down the people closest to him, he was strolling through a battlefield full of some of the most powerful people in one piece, pausing only to OHKO giants and vice admirals.
You're right, we didn't see Whitebeard block one of Akainu's magma fists. Intead we saw Whitebeard tank one, then proceed to pound Akainu into the ground. Akainu is one of the strongest characters we've seen, and he was taken out as if he was fodder.
d
What you also seem to be forgetting is it wasn't as simple as 'Nobody fought Shanks, so he's stronger!' There had just been a giant brawl, with people as strong as Marco, the Admirals, Garp, Ivankov, Sengoku, Whitebeard, Mihawk, Crocodile, Doflamingo, Jozu, Jinbe, Ace, Blackbeard... Nobody could have emerged from that battle in a full state - Shanks appeared after the Marines had just accomplished their goal to kill Ace and Whitebeard, Blackbeard had just stolen Whitebeard's fruit, and the commanders of the Whitebeard Pirates got distracted then incapacitated, blasts of Haki flying around knocking people out. Blackbeard at full health, with a reason to attack, might have fought Shanks. Were the marines to have a strong enough reason to, not have the Admirals being wounded, or almost knocked out, the Shikibukai infighting amongst themselves - everyone was tired and injured. So yes, they didn't fight Shanks. But were the situating reversed there's no way to know that the Marines and BB pirates wouldn't have let Whitebeard call an end to their war...
(Here shanks wins for sure) 
