Here's the screenshots of all three readers from my tablet, each on the same page of the same book at more or less the same font size.
The first one is the Kindle and the second is Bookari. I think the text looks a tiny bit better in the Kindle version, but it's hard to really tell much of a difference between the two. The third image is from Moon Reader with embedded font support turned on. Don't ask me why every single character is in bold text, because the epub isn't calling for it. You can see the other two render them perfectly.
Looking at them all three again, I can't say that I see a huge difference between any of them, but I would definitely say that I have them listed in order of my preference, though I'd have no issues reading on any of them, assuming the weird bold text on Moon Reader could be fixed. Personally, I found Kindle and Bookari, very easy to setup and go, whereas Moon Reader seems to be overly complex. It took 45 minutes of messing around with it just to get the pages to turn like a books rather than scrolling like a web page, and to turn on embedded font support. However, that still leaves a gray screen and all bold text where they shouldn't be and, honestly, life is just too short to spend on something like that, that should be really simple and straight-forward, especially when there are, in my opinion, better options out there. To me Moon Reader is just overly complex and has far too many features that I will never use.
