Answer
We, as Muslims, are taught to use the word ?Allah? instead of ?God?. This is on account of the word ?Allah? being unique, referring to One Independent Allah.
?God? on the other hand, has a feminine ?goddess?, accepts partnership, i.e. ?gods? and also accepts dimunitives ?godlings?. Thus, a word of this type doesn’t properly reflect the qualities of Allah. However, if one is addressing a non-Muslim who is not familiar with the word ?Allah?, then ?God? could be used.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai