Photo sharing

As a very casual photographer, I've been aware of various photo-sharing sites without having used them. Everyone's heard of Flickr, but there are more sites--many more, as it turns out. It's mind-boggling! Among the ones mentioned in websites that review the services are Photobucket, Flickr, Webshots, Fotki, Care2Connect, dotPhoto, Avanquest, SmugMug, MyPhotoAlbum, KodakEasyShare, Picasa, Shutterfly, and Snapfish. Wonder how anyone ever chooses among them? Where's the authoritative review site (I ask that a lot about websites)?