That's just it though. Both are phonetically correct. Otherwise we'd not be discussing it. No bastardization involved.
GIF noun \ˈgif, ˈjif\
Definition of GIF
: a computer file format for the compression and storage of digital video images; also : such an image itself
Origin of GIF
graphic interchange format
First Known Use: 1987
http://www.merriam-webster.com/dictionary/gif
So. Purely a matter of opinion.