Nelson and Rodney lead the 1920s 16-inch comparison

Which 16-inch battleships were strongest in the 1920s: Nelson and Rodney or Nagato?

Probably Nelson and Rodney in the 1920s, though later 16-inch ships change the comparison by the Second World War.

Nelson and Rodney are preferred over Nagato among the 16-inch-gun battleships available in the 1920s. That judgement is specific to the period and does not make them permanent winners across every refit and combat condition. By the Second World War, additional 16-inch classes had entered service. Those later ships changed the field being compared.