American English is more familiar and we have heard it a lot. But for me British English is beautiful, I've been learning British English and its so different with American English. Even British English itself has many different accents depends on the city or area in UK. For example London may has some different pronunciation with Manchester. For beginner, American English is much more safer.
The answer depends on the particular English learner and what they want to do with English. There is no general correct answer. Does the student want to study or work in the US? Learn US English. Want to go to the UK? Learn British English.
If they want to stay in their country, they can learn general English, or the dialect more commonly used in their country.