Defo the blue whale. The sheer size of them amazes me. I'll always remember a school assembly many years ago where our headmaster demonstrated just how large the whale is. Fascinated me. What I also love about them is the mystery of them still. Not a huge deal is known about where they go in the deep blue and it just adds to the excitement I feel about deep sea exploration.
Also this woman I know who is a holiday rep gives tours all over the world and one of her regular gigs is doing a tour in Canada for a month. Doing one of their whale watching events one day, the group actually came across a blue whale. She says its the most incredible thing she's ever seen and at the time while suffering a sprained ankle she said the pain just seemed to disappear as she got up to stand by the boats rail, her mind just is awe of what she was saying. I'm so envious of her experience.
Side note, such a shame that the bloof sound was nothing animal.