GIF is pronounced with a hard g, contrary to the claims of its “creator”, Steve Wilhite.
Steve Wilhite only “created” the GIF format to the extent he didn’t copy it from previous creators. At the time he wrote it, he worked for CompuServe. The GIF format contains the concept of global vs. local palettes, and it contains origin information for frame within a frame. That’s really the extent of the novelty in the GIF format. All of the actual color data is stored within a Lempel-Ziv-Welch compressed table. Wilhite copied the LZW algorithm direct from this seminal 1984 paper and hence from the Unix compress program. I know this, because as a Harvard undergrad struggling through CS175, I implemented a converter between Harvard’s image format and GIF. My program used the guts of Unix compress, along with that paper, to encode and decode GIF images.
In the mid 1990s, Unisys used threats to try to shake down a few companies over its claimed ownership of the LZW algorithm. This is after one of the authors published the algorithm publicly and went to work for another company. As is usually the case in high tech, Unisys’s attempt to screw other companies backfired.
In essence, Wilhite’s and CompuServe’s only practical novelty was simply stamping a copyright notice on the front of some existing technology that they didn’t invent.
So the best we can do is to call it as we would any American acronym, by taking the first sounds of the words that comprise the object. Say GIF, think Graphics Interchange Format.