That’s a great article! At first, it may be hard to know what format is best for what, but your article does a great job of pointing out the best uses for each.
I know you note this at the end of the article, but the PNG tests on the simple image are not optimised. 24-bit PNGs are overkill for such a limited amount of colour. Just testing one size, I found an indexed PNG beats every other format, and I would bet that goes for other sizes as well.
PNG also has gamma correction, although sometimes that is an annoyance rather than a feature. Fortunately, it’s optional. I know this isn’t about the PNG format specifically, but Internet Explorer has a problem with PNG transparency if the PNG is not 8-bit.