If you had asked me a couple of weeks ago, I would have told you that kindle was my favourite commercial application for buying and reading e-books. To tell you the truth, I had never used Play Books before. Let me insist about the commercial thing. I have used several applications through the years. but only as e-readers. They didn't have an option to buy books online.
I knew Play Books existed and that it was pretty good, the problem was that back in the day you couldn't import your library to the platform. It was only possible to read the books that you acquired through it. So I had never even started the app.
But when I revived my lenovo tablet after a long hibernation I started using Play Books and I must admit that I love it, in fact now I am using both (kindle and Play Books) at the same time.
In the kindle I am reading a book about ecological gardening and in the Play Books I am reading "La Bestia" (the beast) by Carmen Mola. I am truly enjoying both the books and the e-reader applications.
The best thing without a doubt is the synchronization between devices, no matter if you are reading on the tablet or the phone you do not have to waste a minute trying to figure out where you were when you left it. Both apps take you to your bookmarks.
And very likely the second best thing would be night light, for reading when it gets dark.