If I had to pick just one line, then probably when Lightoller and Captain Smith are on the bridge talking about how unusually flat the ocean is, Lightoller points out "it will make the bergs harder to see, with no breaking water at the base." You can almost see the gears turning in Captain Smith's head that he should consider slowing the ship down, but the thought doesn't quite form before he heads off to his cabin after ordering Lightoller to maintain speed and heading.
There's also a funny dubbed version of the movie I found many years ago on Youtube, and one of the best lines is when Cal finds the note Rose left for him in the safe and they read it as "you are a stinky poo poo head".