When it comes to simple looks and style, the fat Playstation 3 definitely is superior in my eyes. It had a certain look to it that made it stand out as a next generation console, and just looked like a 'beast' with great capabilities in general.
The Slim is my favorite in terms of reliability, though. I used to have problems here and there with my 60 GB consoles, but have had minimal issues with my Slim.
When it comes to quality, I'd take a Slim over an original. When it comes to style and flare, however, the original would be what I'd put in a showcase.