I'm English. Although I get annoyed often with other English people using American spellings or words, I don't think anyone would think badly of a foreigner using American English. Even a mix of the two will not get you laughed at (maybe misunderstood though if you start talking about jam/jelly/jello or chips/fries/crisps in the wrong way.) If you come to English you will probably be surprised at how bad most people are at speaking proper English.

There are probably more reasons for choosing American English. It's more widely spoken, and for business you are probably (I may be wrong) more likely to meet Americans. You're probably, unless you have an interest in England, more likely to visit America, and watch American TV shows and read American books. The only reasons for choosing to speak English English is the fact that we are in the same continent and English is the original. Once you've learned the differences, it will be easy for you to switch between when you need to. I could easily write American English if I needed to, although I'd probably forget sometimes.