They all optimize PNGs in different ways. For some files one tool is the best, for others another tool. There are even meta-tools like PNGGauntlet that just bru

They all optimize PNGs in different ways. For some files one tool is the best, for others another tool. There are even meta-tools like PNGGauntlet that just brute-force the compression with several of these tools (e.g. pngout and optipng) at the same time. That way, you can be relatively sure that your file will be close to being the smallest possible.