Well amongst the ones you listed, the most aggressive and strong (in a good-natured way) would be Kangin. Yet he is also known for his utterly adorable smile that "makes women wanna protect him!"
Sungmin and Hankyung are strong as well (they know martial arts) but not as strong as Kangin (according to the show: Exploration of the Human Body ^_~, no one is stronger than Kangin). Eeteuk is just nowhere near "aggressive" or "scary" XD.
