I've always used the blue one. It was the main style when I first registered here in 2003, and I didnt really like the white one when they changed it. I find the blue most calm to look at. White gets too bright.
I use the blue skin because it is easier for me to look at. The white one is too bright for 3 am when I am on and I don't really like the green because green just doesn't appeal to me. Other than black, I think that blue is the only good colour for my computer.