AVIF is what many sites now serve because it is the smallest format browsers support, but saving one to disk leaves you with a file that Windows Photos on older builds, most editors and nearly all upload forms cannot read. JPG is the universal fallback. The JPG will be noticeably larger than the AVIF for the same picture, and any HDR or wide-gamut colour is reduced to standard 8-bit.
JPG has no transparency, so see-through areas of an AVIF are filled with a solid colour, white by default; you can change it under Options. JPG holds a single still image, so an animated AVIF does not stay animated. The defaults suit most files. Under Options you can set the quality, aim for a target file size and resize the result.
Camera metadata such as EXIF and GPS location is not copied into the JPG, and the photo's rotation is applied so it stays upright.