Unless you are totally confident about all features of American English which differ from British English, or your text is specifically geared towards an American readership, we advise you to adopt British English spelling. Here are some common differences between the two systems:

There are also individual words which are spelled differently, such as grey and sceptical in British English versus gray and skeptical in American. The word programme is a special case. If you wish to refer to a ‘computerprogramma’ then the word you need in both British and American English is program; for all other meanings, the British English spelling is programme, while the American form is invariably program.