I wouldn’t agree that either is necessarily “more genuine” as @JohnPeyton has suggested. Intonation and emphasis can affect the intended meaning as much as the actual words used.

Additionally, I think usage will differ between different English-speaking regions and countries, with some nationalities being naturally more reserved, and others naturally more ‘gushing’. Thus some will tend to use superlatives much more readily than others, with the result that the former may have to use ‘super-superlatives’ to express greater thanks!

In summary, and answering OP’s direct question:

Neither is wrong and hence neither ‘more correct’.
Both are equally useful, as is just plain “Thank you”, “Thanks”, “Many thanks”, and other variations.
I do agree with @JohnPeyton that “Thank you very much” is a little more formal, and “Thank you so much” is less formal.