Play Books:
+Rendering of fonts and text seems better
+Page turning animation looks and feels really good
+Effortless syncing and downloading of books- seems to be completely automated
-Margins don't seem to get as close to the edges of the screen as Kindle
-Doesn't have the sepia tone reading mode like Kindle (yet!), only B&W/W&B which hurt my eyes at night
Kindle:
+I can preorder books on Amazon.com but not on the Play Store (yet!)
+Sepia reading mode is easy on my eyes at night
+From what I can tell, has more free books, but I could be wrong
-Very easy to accidentally turn a page or randomly goes to a random page and I get lost and have to find my way back to where I was
-Archive and On Device areas are separate. Compared to Play Books it seems like an outdated way of handling things considering how small books are and how much storage devices have.
-Rendering of icons, clipart, images, and even things as simple as italicized words is very poor. (IE: when a word is italicized on my Kindle app the font for that word seems 2 sizes smaller than everything else, and since it's in a seriffed font it's barely readable)
BOOK PRICING: From what I have seen over the past few weeks, the Play Store is quickly catching up to Amazon's pricing. Most of, if not all, of the books in my Amazon Kindle wish list are the exact same price as the Play Store, whereas maybe half of them were a month ago. Amazon may have one or two books that the Play Store doesn't have, but with the Magazines app Google has now, it's only a matter of time before I can switch completely over to Google for comics, graphic novels, etc.