Personally I prefer the american way in both written and spoken english. Just because it comes most natural me. That probably comes of all the things that are american. Movies, TV-shows, clothes, social media, etc. all are mostly produced in america.
To improve my english I like to read english books and watch movies. If you watch a movie with subtitles on Norwegian you can pick up typical american phrases. You can then use those to make your english sound more like you are comfertable with the language.
I can personally work on expanding my vocabulary.