Cthulhu's mainly right about the nuclear ones… They're
still more formidable. ;)
Even after the end of the Cold War. It's true.
these are the old tests before they moved away from the BIG babies…

But Russia's MIRVs are still the best because they're hypothetically matched against the missile defence system.
The USA has a lot of nicely reliable ones though and a brilliant sub fleet… But then it's better not to think about that stuff really :(