OMG I love Niva's skin!!! And KK is right, they are probably the most realistic skins I've ever seen!!
Here is a pic of a sim that I was playing around with one of her/his skins.
The first one is Niva's.
I don't know whose skin this is, but it's pretty good also. But you can seriously see more detail in Niva's skin than this one, although both are nice. I guess it would pretty much come down to your taste that you prefer.
This is the same exact sim, only difference is the skin.
He just makes my belly button smilez!