Which English variety to settle on? British or American?

Xie, you can create your own "variety"!
I know many people who mix British and American English, for example they use a rhotic 'r', but the typical Southern English pronunciation of 'last' and 'half'. This way, you can sound more international. Sometimes, such a variety is called "Mid-Atlantic", because it incorporates elements of both British and American pronunciation.

>>''California really doesn't have its own version of US English''

this is not true at all:

http://en.wikipedia.org/wiki/California_English<<

The article isn't wrong at all, but I'd like to point out that many Californians do not have the California Vowel Shift therefore sounding Western, therefore sounding pretty neutral.