When I bought my first Kindle, the keyboard model, I was hellbent on getting a case and I found one for cheap that I thought I liked well enough. But I found myself taking my Kindle out to hold it while I read, and when the case made permanent scratches all up and down the sides, I decided I didn't want a case, I wanted a sleeve. I didn't buy one, I made one, and then when I bought the Paperwhite I just cut it shorter and mended it and it's perfect.
This may be weird, but I like to run my fingers up and down the bezel of the Paperwhite while I read (I like the smooth texture of the plastic) and across the rubber backing. I can't do that with a case and the sleeve I made protects the Kindle from dust and scratches, but can still hold my Kindle while I read.
Do you guys prefer your Kindle in a case all the time or naked?