I was on the fence between the White/Silver and Black/Slate models. I eventually went with the silver as a change as every other iOS device I've owned has been black front. Second reason which pushed me were the reports that a lot of slate iPhone users saying that when scratched hard enough, the slate comes off to reveal silver beneath. Saw this in person with someone's iPhone 5. Figured this must be the case with the iPod too, so I decided to stick with the silver.
Looking back now the slate does look a tad sleeker, especially with the device powered off. However, looking at new screenshots of iOS 7, white front may look better and pay off in the end. I'm sure black front looks geat too though. To each their own!