Steffan

I actually prefer this to Stephen / Steven; but in the United States, Steffan never really caught on as a name. You might see a Stefan (steh-FAHN) here or there, and that's a big "might," but not a Steffan. And the nickname Steff is typically seen as either wholly feminine, or pretentious and prattish (see the character Steff McKee in the 1986 film "Pretty in Pink"). Which is a shame, because Steffan is a good name.