I'm pretty sure it's pronounced "ping" now since GIF is rolling slowly to the dustbin. Of course I'm sure the creator of the PNG format would say it's pronounced "pong". At least that would make sense. The whole jiff joke was never, ever funny. The reason people use a hard G is because that's what makes sense given the wording of the acronym. Unless I've been pronouncing "graphics" wrong this whole time?
Slowly is a bit of an understatement. The format has been in widespread use for a quarter century.