Both are the same genus (Athene) so they’re related, but not quite as closely as they look. The Spotted Owlet is currently thought to be the closest genetically to the Little Owl. Some believe Burrowing Owls should be their own genus, but I haven’t gotten to look into that more.

As long as we’re just going visually, the 2 would probably be the best match, but in most other ways the little guys are surprisingly different.