The Abomination in all his bloody beauty. Or the Glutton if you make it green since there's a bunch of color to choose. I always thought he was a pretty cool monster, more funny than scary.
I hate how he always seems to jump in my back everytime i'm in Stratholme tho.
To change colors, you need Pepakura Viewer (link right->)
Go in configuration, texture configuration and choose one of the texture that's in the file.