Which is easier to master? American English or British English?

This includes all native slang.

If you ask an American, I'm sure they'll say theirs, same with a Brit.

LOL they're pretty straightforward if you already know English

Wad u say u bloody wanker ;) Did I do it right?

Including native slang? American English. British English is so much more complex this has way more than one type of slang, and many of it regional and based on cities. Not to mention half of them aren't even similar in anyway shape or form.