Comparing the 128x128 images with the original:
Discrete Wavelet Transform
Without looking at these very hard, it is difficult to see differences. The Pixel Skipping image has some color artifacts which show up as green dots all over the image. They are most obvious against constant color backgrounds, such as my shirt (light blue, on right side).
The Pixel Averaging and DWT images are hard to compare unless you blow them up. Then the DWT image can be seen to have better color gradations and fewer color artifacts. However, both images are very good at the regular size.