Soft G, Jiff sound.
GIF (with a hard G) just doesn't sound nice.
To me, it sounds more like a guttural noise than a word.
But that's not a major problem anyway, since .gif isn't a word to begin with. It's an acronym.
Gif just hits me as a rough and unpleasant sound, so I like Jiff instead.
To be fair though, there's not a lot of circumstances where I actually use it as a word in speech.
Most of the time that it comes up, I'll be on the computer and I'm just typing it in.
If it does come up in speech, I'll probably try and say "Dot Gee Eye Eff" so that someone gets what I'm talking about immediately.