What is GIF?
GIF is thirty-eight years old and refuses to die, because it animates and everything opens it. The cost is its palette: 256 colours per frame, so photographs come out visibly banded. Transparency is on-or-off per pixel, with no partial opacity.
What is WEBP?
WebP is Google's image format for the web, and the rare one that does both jobs: lossy compression that beats JPEG at the same quality, lossless compression that beats PNG, and an alpha channel either way. Every current browser reads it; older software often still does not.