What would I benefit most from?

New to the hobby, love painting the models and playing for fun. I am in the infant stage of building an army. All I have are a squad deathwing knights and a redemptor dreadnought. I follow the rule of cool and get what I like. What's most beneficial in all situations a repulsor executioner or a brutalis dreadnought? Following my rule of cool, I like them equally.