MOV does not play reliably on Windows, Android, smart TVs or in many upload forms. AVI is read by old Windows software and some standalone players. MOV is at home in recording and editing on Apple devices; AVI is the usual choice for old Windows software and capture devices.
The defaults suit most files. Under Options you can lower the resolution, trade quality against file size, remove the sound 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 AVI cannot be written 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.