What is AVIF?
AVIF is a still image squeezed with the AV1 video codec, and it compresses harder than anything else in wide use - frequently half the size of a JPEG that looks the same. It handles transparency and high dynamic range. Support is good in browsers and patchy everywhere else, which is usually why people convert out of it.
What is TIFF?
TIFF is the archival and print format - lossless, high bit depth, and flexible enough to hold multiple pages in one file. Scanners, publishing workflows and document archives lean on it heavily. Browsers have never displayed it, which is why it is offered here as a target rather than a source.