It doesn't matter. Learn General American (GP) or Received Pronunciation (RP). GA and RP are more similar to each other than either is to the many local accents that you'll hear in England, to say nothing of the rest of the United Kingdom. Also, you should imitate the pronunciation of whatever listening material you like.

And, I'd like to add few more things here. Just try to learn standard English pronunciation either American or British. Both are right and would boost your English. Use Oxford Advanced Learner's dictionary. It is really handy and easy to use. Learn PHONETICS as well. Once you learn phonetics you can master the pronunciation.