Some arguments that people keep bringing up that are all wrong and carry zero weight in this discussion:

• The creator says it's JIF
• It's like Gift, but without the T
• It's like Giraffe, but without the raffe
• It stands for "Graphics Interchange Format" so it's GIF
• My dictionary says it's GIF
• My dictionary says it's JIF
• Obama says it's GIF
• Giphy says it's GIF

Ultimately, language is very dynamic and changes all the time. Words change their spelling, their meaning and their pronunciation too. Dictionaries tend to lag behind a little bit, but the fact that they publish a new version every year signifies how much languages change. The creator of a word can coin a pronunciation, but ultimately has zero control over whether it will be adopted or not.

So therefore whichever way most people actually pronounce it is by definition the correct pronunciation. And the polls done on this subject are pretty clear, showing that GIF is the preferred pronunciation, chosen by up to 70% in North America and over 80% in Australia and the UK. This depends on which poll you use, but in general the split is at least 2:1 in favour of GIF, and over time the usage of GIF tends to trend up over time.

So ultimately, the one true pronunciation is GIF, as decided by the people as a whole. However, most dictionaries do list JIF as an accepted alternative pronunciation, due to the not insignificant minority pronouncing it that way.

In other words, just choose which pronunciation you prefer, and use that. And try to avoid the pointless debates people like to have on the subject, filled with arguments that don't carry any weight whatsoever.