What's the best iOS app for reading and annotating sideloaded EPUB books?

Barnes & Noble NOOK is a compelling option for iOS users seeking to read and annotate personal EPUB files. The app allows direct sideloading of EPUB and PDF formats, enabling access to a wide range of content beyond the built-in store. Once imported, books benefit from features like adjustable fonts, themes, and page-turning animations that reviewers praise for their smoothness. Annotation tools include highlighting, note-taking, and bookmarking, which sync across devices via a Barnes & Noble account—handy for readers switching between an iPhone and a Nook tablet. However, some users report occasional glitches with editing older annotations after app updates, a minor but noted inconvenience. For real-world use, this setup suits academics or hobbyists building a permanent, self-managed ebook collection. The emphasis on digital ownership is a key draw, as purchased or sideloaded books remain accessible without risk of removal, addressing concerns common in subscription models. While the audiobook section lags behind specialized services, the core reading experience is robust, making it a solid choice for EPUB enthusiasts.