Since the poll has already been created by myself (and @Concavenator Wrangler) in the past, I wanted to dig a little further into the discussion. This is particularly interesting since this fight certainly happened at some point.
For my opinion, I'll copy one of my comments from the other thread.
As far as I'm concerned, there are four factors that would impact the battle. Size, Bite, Intelligence, and "other advantages." We don't know enough about either animal to figure out much else.
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Size- I'll go with the 2019 15.3-meter estimate for C. megalodon. While some estimates are significantly larger, others are significantly smaller. Also, the 25-meter estimates are straight up bogus. As far as the Livyatan goes, it appears smaller when scaled to Sperm Whales, but larger when scaled to its closest relatives. We can debate this if you want, but I will give this a tie, since we are not quite sure how large either of these animals got.
Advantage: None
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Bite- This is the most common "rallying point" for people who think megalodon would win. However, to date I have failed to find any scientific paper estimating Livyatan's bite. Based on how robust its jaw was, it might actually have had a higher bite than megalodon. All this is speculation, and at the end of the day, both clearly had a very high bite force. Therefore, I think its fair to assume that whoever got the first serious bite would win.
Advantage: None
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Intelligence- We could start another thread about what the smartest animal is, but to just state the facts, whales have the largest and most complex brain on the planet. Whether this means they are the smartest or not is up for debate, but Livyatan was clearly smarter than megalodon. It would be better at making tactical decisions based on its situation, whereas megalodon would act on impulse.
Advantage: Livyatan
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Other Advantages- I will look into two here. First, Livyatan's need to go to the surface to breathe. Second, could one sneak up on the other?
Much is made of Livyatan being an air breather, but, in actuality, this would not be a significant factor. Sperm whales can hold their breath for well over an hour. Livyatan might not have been a deep sea hunter, but even Orcas can hold their breath for around 15 minutes. Given Livyatan's intelligence, it would surely take a breath before the fight began.
Second, I don't think either animal could sneak up on each other. Sharks have excellent noses, and can detect electrical impulses. Whales can also use echolocation. Livyatan had a large Spermaceti organ, meaning that it was certainly no exception.
Advantage: None
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There you have my opinion. Intelligence, which people often see as a "useless" factor, is, in my opinion, the only area that one of the two animals has an advantage in. I think it would be just enough to tip the balance decisively in Livyatan's favor.
While most Paleontologists avoid these discussions, this fight certainly happened at some point, so Professor Donald Prothero commented on it in his book "The Story of Life in 25 Fossils" when he stated "It [Livyatan] could have eaten megalodon if it wanted to."
Either way, I don't think this has been covered in sufficient depth, so I'd love to hear what you have to say.