I don't have a crystal ball so I can't guess who will win.
Google has gotten much better, the eReader app works great but it has few features and optionsis almost as usable as the kindle. The google sync is far better and the conversion between PDF vs ePUB is near perfect. Google books can also be read on other devices that support Adobe DRM. Google DRM does not seem to be limited to a device so I can read a book on as many Android devices I have registered to my account.
Google books is integrated nicely to their store and to the Android platform. However Amazon is just as well integrated and have excellent customer support.
Right now the eBook market is too young to determine a clear long term victor but both platforms have some distinct advantage over the other. I have not bought Amazon books in some time and have never bought a book from Google up until a few months ago. I purchased the "
Princes Bride" for $3.99.
I don't know if it's a promo but it was under their
Sword Play starting at $3.99 banner in their market app