Choosy mothers choose gif.
As a grizzled vet of the post-2004 GIF community let me state definitively, this is a non-argument: the gif creator's own preferences have been trumped by the street (which actually uses his product on a daily basis), and only posers say "jif" now.
"Shadus" makes a good point: "I’ve always pronounced it GIF (Graphics Interchange Format) same G as Graphics…"
I've been using the soft g for nigh on twenty years. I don't know that I can re-program those bits at this point.