Who is worse: Pharaoh or Abu Lahab?

Engaging in and debating such matters is a waste of time and effort. A Muslim needs to know whom to emulate, not who the most disbelieving people are. If the intention is to know them in order to be wary of them, then there is no harm in that.

Pharaoh was more disbelieving and rebellious than Abu Lahab. He claimed Lordship and divinity, exploited his people, misguided his soldiers, showed enmity towards God's allies, and tormented people. No tyrant was mentioned in the Quran as frequently as he was. Allah Almighty says: (The Fire, they are exposed to it morning and evening. And on the Day the Hour appears [it will be said], "Admit the people of Pharaoh to the severest punishment.") Ghafir/46.

As for Abu Lahab, he disbelieved in Allah and His Messenger and died upon his disbelief. He did not inflict harm upon the believers as Pharaoh did.

Ibn Taymiyyah said: "And He [Allah] did not mention about any of the disbelievers, regarding their disbelief, tyranny, and arrogance, anything greater than what He mentioned about Pharaoh."