Of the four posted, the Ash is the best in my opinion. The other three aren't bad, but they aren't necessarily great either. White is probably one the worst colors to work with, because if you make it too dark, it looks like too grey (and thus, the contrast is too great between the two colors), and if you make it too light, you can't tell the difference. I would try and add more shades of white to the jacket, to perhaps try and even out that contrasting. I also find it funny how the person is scratching his head.
The yellow sprite is just looks weird. You basically just head-switched, which isn't the best thing to do. If you're going to head-switch, at least try to change the expression on the face to match the body language, it makes the sprite much better that way.
As for the female trainer, probably the best of the those three. The dress could have used more shading, but other than it, it's pretty darn good. The hair shading is what bugs me the most though. It's just too square. Try to round out the shading.
