If the meaning is quantity, then they can be used interchangeably: - i have had enough to eat and I have had a sufficient amount to eat are the same However, enough can also be used in ways that sufficient is not used: - Enough already - exclamation meaning Stop it! As far as which is more common, enough is the more informal way of saying things, and is the most common. Hope that helps!

When comparing two alternatives, one may be more or less common. I think I've written enough. My first comment would have been sufficient.