I've begun to realize that by doing this kind of comparison I'm paying a lot more attention to the devices than I normally do. The usual thing is I pick one up and get lost in it's story and forget the device is even there until I put it down. So I'm aware of impressions while picking it up, turning it on (or opening the cover) and while turning it off and putting it down. Now I'm making myself stop and really think about it from time to time as I read. I hope this doesn't become a habit but for the moment it's fine.
I've added a couple of factors to my opinions about the two devices, both of which are pro-Kindle. The first is that I keep running into little, not very important bugs on the Kobo. One example that recurs from time to time is that the border around the definition of a highlighted word will be incomplete. I'll see about half of the border, usually on the left-most portion of the definition and the border on the right will be gone. This doesn't make it difficult to read the definition so I've probably been seeing it for a while and didn't notice. I did check a couple of other books and I was able to see that bug in them, too. As a reader I don't really care much. As a former programmer and project leader I think whichever programmer at Kobo wrote that code needs a pay cut. It seems to happen about one time out of every 8 or 10 times I look at a definition. I haven't looked for it yet on the Kobo Mini. Maybe I won't. I've had enough devices disillusion me.
Another thing I've noticed is that the Aura's kerning is often uneven. Not always and I haven't really looked for patterns to determine when it's off. Again, this doesn't bother me enough to have noticed it in the past so it's a minor thing.
I used to have a home computer, a Radio Shack Color Computer, that didn't have a GUI. In fact this was before there were GUI's. But it did have one word processor that put the computer into graphics mode and drew the letters on the screen. This was before the days of True Type fonts, etc. and it didn't look great but it looked a lot better than the monospaced text I was accustomed to. Anyway, I was fascinated that the letters weren't evenly spaced and I asked around about that and that's when I learned about kerning. I was curious about it so I wrote a little program that would, in graphics mode, draw letters on the screen, spacing them proportionally, to see how that was done. My little test program never produced anything that looked as good as that word processor and I worked pretty hard at improving it, trying to understand how it could be done. So I know this is difficult stuff. The thing is that Kindle does it very well. Kobo does it fairly well most of the time and is sometimes sloppy.
These aren't the only bugs but they're the ones that stick in my mind. The rest were a bit obscure and might have more to do with my not understanding how to prepare a book for the devices using Calibre than anything the programmers of the devices did.
None of this overrides the fact that so far I'm really enjoying the chapters read on the Kobo Aura more than those read on the Kindle Voyage. Not a lot more, but the way it fits my hand is so much better that it makes up for this other stuff.
Kobo, in case you happen to run across this post, if you'll make a Kobo Mini with a front light I'll buy one and you can be as sloppy as you like programming it. I promise!
Barry