IANA has reserved example.com, example.net, and example.org for use in documentation as examples.
It's useful but not informative, It's very safe that you cannot registrate on that domain.
Safe. Not very useful, but I guess it could be entertaining to stumble onto.
My favourite site, it's informative if its that kind of thing you like, it can also be informative in other ways, you can post news topics etc.
example.com should make every page no 404 errors, because it's for example, and it makes every examples work