I remember reading that one of the creators of the GIF came down on the side of the soft Gs. Some would say that being the format's creator gives him the right to specify its pronunciation, but I prefer to apply cold hard logic (of sorts) to the question:

  1. GIF is an abbreviation of "Graphic Interchange Format"
  2. "Graphic" is pronounced with a hard G
  3. Ergo, the G in GIF is a hard G

Here in Ireland, Jif is a brand of kitchen cleaner, and also a brand of lemon juice.