Jif, but both pronunciations are correct and if you don't accept that you are causing dying children in Africa
Also because reasons here's some common points mythbusted
The g in .gif stands for "graphics", which is pronounced with a hard g
It's not unusual for acronyms to have pronunciations that differ from the words' pronunciations. For example, the U in SCUBA is for "underwater", but SCUBA is pronounced "scoo-buh", not "scubba"
The creator says it's pronounced with a soft g
Well, I'm sorry, but if you invent a word, you have no control over how the pronunciation is changed. Covert, pronounced like overt with a c, used to be pronounced like cover with t, for example.
gif/jif sounds stupid to me
Go forget yourself