Using stb_image decreases loading times for images by around 25% when compared to pnglite for me, but this should be tested with other compilers, computers and images.
This would also allow using other image formats in the future (right now only the PNG implementation is enabled).
pnglite is getting old and the author recommends stb as well.
See https://github.com/dankar/pnglite and https://github.com/nothings/stb