Depending on your needs, Picassa and SmugMug are the best in class for photo storing and sharing.
Some things to consider are the resolution that is stored and availability of those images. Snapfish can and will downgrade images over 9 megapixels. You want a site that preserves your image exactly, and allows you or those you share with the ability to retrieve those images in their original size.
Unlimited storage, video storage, and sharing and privacy controls are also items to consider.
Picassa is free with some unique limitations, namely in ability to password protect shared files in multiple ways. Smugmug isn't free, but at $40 a year you get a lot of nice extras that may not be too exciting for the average person.
I use smugmug and love it. My main concerns are online storage, I want my pictures backed up and protected exactly as they are on my hard drive now. I also want to share pictures securely with just one password and no logins or memberships to join for family. Basically, can my mother in law go to one address and enter one password and have access to all our pictures and videos we choose to share.