"One of the things that make the United States special is its diverse and varied linguistic background. You might think people speak the same English you and I know, but no. The number of different accents spoken in the US and the degree of lexical variation is just fascinating. Language variation is probably one of the most exciting stuff that linguists concern themselves with. One of these is Joshua Katz, a Ph.D. student of statistics at North Carolina State University, who took on the job of mapping the linguistic variation of the US and published them in a book he titled Speaking American. Here are some of the coolest maps from his collection."
There are many videos on this question. American videos take the view that American English is a better choice and British videos take the view that British English is a better choice. This video is from an Australian. I agree with most of her points. She argues based on the number of countries adhering to one standard or the other. While it is true that more countries adhere to the British standard, the fact is that in shear numbers, the number of speakers of American English is much larger, the influence of American English on media and business is much larger, and the comprehension of American English is more universal (due to the media and business influence).
Nevertheless, she makes a good point. If your mission includes impressing a British university for the purpose of studying there, the British are more strict in what they consider to be proper English. American universities, on the other hand, take a more holistic view on what constitutes proper English - a view more consistent with the position of linguists: all varieties of English are equally valid. In the USA, you are free to use British or American spelling and grammar. In the UK, a country with a much smaller population, universities expect you to conform to their own British dialect that they presume is "correct".
American English branched off from British English during the early colonial years of North America. Since then, it has evolved and flourished into its own and does not look to the English across the ocean as an authority on the English language. With a much larger population and greater influence upon the world, American English has become a source of new vocabulary for English around the world. While the powers-that-be in the UK imagine themselves arbiters of the English language, these Americanisms creep from the bottom up into British English. In reality, at this point in history, American English has a greater influence on the English language globally - not British English.
