I don't use any of those services but I do have limited experience with various ones. I would recommend jAlbum
www.jalbum.net if you are always going to be sending photos from the same computer. You get a certain amount of free space for image storage and it's pretty easy if you want to try fancier types of galleries.
I think Flickr is pretty user friendly, and I'm almost certain that iPhoto on your Mac will let you enter your flickr login and password like you can for Facebook and it will automatically send up the photos you want to use. Flickr will work well from any computer.
Photobucket is pretty easy to use. I used to use them in the past before I started creating my own. Photobucket will also work well from any computer.
