As you can see, no one program is best for every type of Web graphics file. In fact, the differences between the programs was not huge when it came to file sizes and some would perform better with some images than others.
In terms of usability, Photoshop and Fireworks both give multiple previews, so you can directly compare what a file will look like with different formats and compression techniques. Ignite can do this too with a bit of coaxing. ProJEPG, PaintShop Pro and SmartSaver give 'before and after' pairs but PaintShop Pro's is a little too small to be useful.
When it comes to the crunch, the file types that I find most useful are the very small (low bit-depth) GIF for graphic images and JPEGs for photographic images. With JPEGs, I tend to err on the side of quality rather than going for the smallest possible file size. Much as I would like to, I don't use PNG files generally because of the patchy support for the format.
For small GIFs and PNGs, Ignite consistently produced smaller files sizes than its competitors. We are only talking about a hundred bytes or so between best and worst though. For JPEGs, Fireworks and ProJPEG performed best with these particular images and their before and after previews made it easy to find the threshold point.
Using the correct file format for any particular graphic is more important than the program you use to create it. For GIFs, it mostly comes down to getting the lowest possible bit depth. For images that have only two colours, you can come right down to 1-bit. If there are two colours and anti-aliasing, you probably need 3-bits (8 colours). JPEG's lossy compression is always a trade-off between quality and file size but there are a few tricks you can play to squeeze them just a little bit more, like using a small degree of smoothing or adjusting sub-sampling types and values.