I agree that the manner this was presented at the 2013 Webbys, which kickstarted the debate, was jokingly, but the specifications have always recommended “jiff” since the format’s inception, though also a bit jokingly:

Wilhite and the team who developed the file format included in the technical specifications that the acronym was to be pronounced with a soft g. In the specifications, the team wrote that “choosy programmers choose … ‘jif’”, in homage to the peanut butter company Jif’s advertising slogan of “choosy moms choose Jif”.[3]