The same, just British is more fun :)

Hi!, You should be more concerned about the <em>culture</em> you want to learn or emulate.  When we speak another language we sort of imitate other people, and the <em>way </em>people talk is the way people <em>are.  </em>If you can make that initial difference you'll begin to find one variation more difficult or less appealing, and you'll start <em>imitating</em> the British or the Americans... Otherwise, you can always stick to a more General Standard pronunciation.

R

I'd say DEFINITELY the American English; despite the fact that the American English has been branched from the English spoken in England. Though here in the states, we do not have that English accent and we do not use the words used in the old English. For example, you'd rarely hear an American use the word "Rubbish." 

So, I'd say it would be MUCH easier if you'd start with the American English.  Good luck! 

The only major difference in pronunciation is the letter 'r'. If you struggle with the English 'r', then I'd go with British English because they don't use it at the ends of words.

For me, The American accent is easier to speak, but I think British is more casual and beautiful accent.
I speak American but I hope I convert to British :D