GIF is limited to 256 colours and produces very large files for anything longer than a few seconds. APNG animates with full colour and smooth transparency, which GIF cannot do. GIF is at home in short looping clips and reactions; APNG is the usual choice for animated stickers and graphics that need real transparency.
The defaults suit most files. Under Options you can set the frame rate, set the width and trim the start and end. This is demanding work for a browser: a long or high-resolution file can take several minutes, and your device does all of it, so keep the tab open.
This pair uses the compatibility engine, ffmpeg built for the browser, because GIF is not handled by the browser's built-in codecs. It is a one-off download of about 10 MB that the browser keeps, it is slower than the built-in codecs, and it takes files up to 1 GB. The result is a looping animation of at most 30 seconds, counted from the start point you set under Options. The GIF's own frame timing is kept unless you choose a frame rate, and the picture is scaled down to 480 pixels wide at most, never enlarged. Unlike a GIF it keeps full colour and smooth transparency, and it has no sound.