I've been using several ebook platform: Amazon possesses Kindle, Apple possesses iBooks, Rakuten possesses Kobo, and honto.
It is one of my favorite hobbies that think about "what ebook platform should I use".
(My another favorite hobby is thinking about "what credit cards should I use", just my two cents.)
I usually use ebook reader app designed for iOS on my iPhone 7 Plus. I'm not going to use ebook reader devices like Kindle Paperwhite. So I don't consider if a particular ebook platformer provides physical reader device or not.
Amazon Kindle would be the best ebook platform. But I want to avoid amazon if possible, because I'm concerning if amazon becomes only one ebook platformer in the world.
Amazon Kindle store looks not very interesting. Initially I have to discover books by myself. Search works fine, but it works fine only if I know the keyword to discover books I feel interesting. Their book-to-books recommendation is very interesting, but store itself doesn't recommend good books so much. Regardless of the attraction of the store, customers' review is most informative, rather than any other stores.
I like iBooks store. It is well designed for customers who want to discover something interesting. It's curated book lists looks fun. I usually enjoys finding and buying ebook at iBooks store.
I also like iBooks app. It is the most easy to use ebook reader. But iBooks is available on Apple's devices only, so to read my ebooks, I have to keep using Apple devices. In addition to that, iBooks doesn't allow readers to export highlights and notes. It is very inconvenient.
Kobo app has unique features. The app counts accumulated progress of reading. If reader achieves something, app unlocks badge. In my opinion, those features are designed to encourage readers to read more. It sounds interesting to me.
But Rakuten Kobo store doesn't look attractive. The tree-style genre structure bothers me. They shows banners to emphasize some books, but I feel them just an advertisement. I don't find any editorial intention from the banner.
honto has a unique history. They have been linked up with real book stores. I want to support them, and hopefully want to support real book stores through using their store. I'm not sure if it is possible though.
Their app is not very good. But their store is very interesting. They introduces many books in various ways. I can browse their curated book lists long time. In addition to that, they offers discount very often. So that if I buy ebook from their store, I have more chance to buy it with most inexpensive price.
I enjoys this my hobby in years. Probably I will keep buying ebooks from several stores in a whim. Obviously, having ebooks on several platform is not a good idea. If you forget which platform is used to buy an ebook, it is a little hard to find it. You might buy same ebook again, without knowing it. Digital bookshelf should be one place. So I don't recommend you to use more than two ebook platforms at the same time.