I compared my K3 with my Sony 350 and Kobo Touch. I used fonts that were as close to the same as I could find. The text was sharper on the K3. This comparison was in my home and not in a retail store. If you compare devices in a retail store you might be surprised that they look different in your home. Retail stores tend to have a lot of fluorescent lights and can have a lot of natural light as well which tends to be much brighter than the typical home.

So two points to making good comparisons: 1. Use the same or very similar fonts, and 2. Compare in lighting that is very similar to where you read most of the time. Otherwise you are wasting your efforts.