As adjectives, these words have the same meaning - the opposite of 'slow'. There is no difference in meaning between the two words. In most cases they are interchangeable.
However, when it comes to collocations (which words tend to be used together with other words), they are not always interchangeable. We say 'fast food', for example, but not 'quick food'. We'd also say 'I'll have a quick look at this' but not 'a fast look'.