The Kurukshetra war · Mahabharata questions
Who was the strongest warrior in the Mahabharata?
The epic never settles it. Bhishma rates himself first among the Kaurava commanders, with Karna half a ratha by his reckoning; Bhishma, Drona and Krishna all name Arjuna the finest archer; Bhima is the strongest man; and Krishna repeatedly says no one could have beaten Bhishma or Drona in a fair fight.
The Mahabharata argues about this inside its own pages, which is more interesting than a verdict.
The epic has a formal ranking system. Before the war Bhishma is asked to rate the warriors on both sides as ratha, atiratha or maharatha, according to how many opponents each can fight at once. He rates himself and Drona at the top, calls Karna a half-ratha, partly because of the curses hanging on him and partly out of open dislike, and Karna in fury refuses to fight while Bhishma commands. Duryodhana counsellors dispute the ranking on the spot. So the epic best-known league table is delivered by an interested party and immediately contested.
On archery the text is more consistent. Drona says Arjuna is the finest bowman he ever taught and that none surpasses him. Krishna, who has no reason to flatter, says the same. Arjuna alone holds the divine weapons gathered from Shiva, Indra, Varuna and Yama, and alone survives every duel he enters. Against that, Karna fights Arjuna to a standstill more than once and is defeated only when his chariot wheel sinks and his mantra fails.
On strength of body the answer is Bhima, who kills Bakasura, Hidimba, Jarasandha and Dushasana, uproots trees, and breaks Duryodhana thighs in the last duel. Duryodhana himself is the better trained mace fighter, taught by Balarama, who says he is the finest he ever taught.
And the epic keeps naming people outside the war as greater still: Parashurama, who taught both Bhishma and Karna and could not defeat Bhishma; Bhishma himself, who fought Parashurama for twenty-three days without a result; Barbarika, who was asked to give up his head before the fighting started because he could have ended the war in a moment.
The honest answer is that the Mahabharata deliberately refuses a single champion, and every ranking in it comes from a character with a motive.