Pros:
1. English is spoken in more countries than almost any other.
2. It is one of the five most spoken languages as either native, second or third language.
3. Its flexibility allows it to say more concepts and ideas than any other language; it has the largest vocabulary with more than 800,000 words.
Cons:
1. English has horrendous grammar, making it difficult for non-speakers to learn.
2. English has little or no phonetic spelling, etc. etc.
3. English is seen as a language of imperialism, first the British and now the Yanks.
4. English is fading language as western influence fades. Within decades, the number of Spanish speakers in South *and* North America will outnumber the English speakers. As well, South America is a rising economic power. In time, Spanish may replace English as the "global language". Even Arabic may be more useful, since it's spoken from as far west as Morocco to as far east as Afghanistan and is the Lingua Franca of muslims.