It's not up to us, really. You're the one who is going to have to learn it and apply it from this day up until the end of time. So, which one do you like? Consider these,
- the percentage of people in the world who speak a variety of British English; e.g., European countries, Australia, Canada, India, China, the Philippines, and more) out number those who speak American English.
However, there's also opportunity and exposure to contend with.
-American English is popular because of its Media. Media is today's Shakespeare. Everyone in the world watches USA movies, buys USA brands, and listens to USA music.
-differences in pronunciation and vocabulary shouldn't impede effective communication. But will other speakers be able to understand your accent? Which variety of English works best for you?
-how many British or American English teachers will you have access to? If you choose, say, to study American English, and your university hires a British native speaker, how will you fare?
-If it's not good, as you say, for an English major to speak a fixture of English, then what say you about Chinese nationals who speak both Mandarin and Cantonese, or Chinese who speak more than one dialect of Mandarin; i.e., Heilongjiang and Beijing? Variety is power. After all, isn't Chinese much like English in that both have more than one dialect?