Kindles use what appears to be a slightly modified version of the Caecilia font. Because my eyes are not as young as they once were, I modify my mobi files to display the text in all bold
on my Kindle 3. I wanted to see how this looked on the Kobo Touch and started out using Lexia DaMa Bold. It is a bit different from Caecilia, but close. Tonight I was able to locate PMN Caecilia 85 Heavy (http://fontpark.net/en/search/Caecilia/1/
), which is closer to the Kindle Caecilia and bolder than Lexia DaMa. I installed this font on my Kobo Touch and it is very close to the bolded Caecilia that is displayed on my Kindle 3. Check out the photos below.
This is the closest I can come to showing a comparison of nearly the same fonts on both readers under the exact same lighting and as close as I could manage to attaining the same font sizes. The two readers are very close in how they render the text. However, I think the Kindle 3 does a better job of rendering the text as it definitely appears a bit darker in real life and it is certainly much more consistent across the screen. That is, the Kobo Touch tends to render text lighter in random areas of the screen than in others. I don't notice that with the Kindle.
Though the Kindle 3 currently has the edge with this particular font, I still think the Kobo Touch has potential as text rendering can be enhanced through firmware changes and Kobo seems willing to make improvements.
Two caveats about using PMN Caecilia 85 Heavy on the Kobo Touch. One, it is bolded normal text only--no bolded italics. Two, it doesn't render well in kePubs, it only renders as shown in the photos in sideloaded ePubs. Great frustration there as kePubs seem to have lots of issues currently.