There are many photo sharing sites on the web these days. However there are differences between them. Some are easier than others, some have more options. It is hard to choose between them. For example. Flickr offers 100 MB of free storage. Picassa offers just 1 GB of storage space. Through Picasa, you can do basic image editing (like crop, rotate, color adjustments, etc) and then upload the edited pictures online. But when using Flickr you can interact with the photographs. Flickr turns an image into a virtual whiteboard where people can scribble text notes.
Those are some of the differences between them. Use them both and have fun!