Apple have Siri, Microsoft have Cortana and Google have Google Now. Which one is better is a discussion that never ends. After using all of them I personally think that Google Now is slightly better than the competition. And just to be clear, I’m not saying this because I’m an Android fanboy. My opinion is completely impartial.
Google Now, that started as a way to simply search Google, has evolved a lot over the years and has become much more than just a way to look stuff up. It is a full fledged personal voice assistant now. Being accessible from any screen adds another level in its functionality.