Which sentence is more formal?

 - In 2012, SpaceX made a splash by becoming the first private company to dock a spacecraft at the International Space Station.
 - In 2012, SpaceX drew a great deal of attention by becoming the first private company to dock a spacecraft at the International Space Station.
The second sentence is less formal. You can tell because it uses an idiom (made a splash).
The first sentence uses formal language in place of the idiom, so it is more formal overall.