It doesn't have to be either, or you go the other way and cut the cable entirely and get a media player with a Plex/XBMC front end. You will still received gimped quality TV but at least it will be free from a cable subscription.
You can use your Apple TV if there are some subscription services you want, e.g. NBA League Pass, NFL game pass, or etc in full quality. This might help cut your cable bill in half, add Netflix and you've got an adequate alternative for Showtime movies, and etc if you don't want to be bothered with downloading.
For all your other channels you can either go over the air or the first option with Plex/XBMC in finding IPTV channels that will meet your needs. The biggest drawback with Plex/XBMC channels is that you don't get the replication of a channel surfing experience and it can be a little more painful to find what you want, but most of it IS there.