With a soft g (jif)
With a hard g (gif)
Out of the 2, this is the one I prefer.
As in "gift".
When was the last time you heard someone say Jif? Doesn't make sense. If some random stranger said jif to me I'd smack him/her in the face.
A Gig is a Graphic Interchange Format, and you say Graphics with a hard G, so why would you change it so the abbreviation is pronounced with a soft g? it doesn't make sense.