Since it became the thing of the week. Let’s move to a 1v1 which probably many will not be able to come to an agreement.
The Lichking in his prime vs Deathwing in his prime
It was highly debated many months back in the official forum , but with some new informations from chronicles and other sources maybe the tides can turn now.
Personally I would go with Deathwing since he is the only being known to survive a direct hit by the dragonsoul which he had to be stripped of all his armor beforehand to even be get serious injured by it . I couldn’t imagine that the lichking has any attacks on that power level but I am not the most knowledgeable when it comes to lore