Hmm...probably SwiftPublisher would work best for newsletters, booklets, pamphlets, and documents needing images. I think Nisus Writer Pro would work better for book publishing. It's more for that than the easy layout and placing objects, etc. I think it has better hyphenation options. It also deals with bookmarks, line numbering, table of contents, etc.
They are quite different. That was one nice thing about Pages, you could do layout type or word processing type documents with just the one app. It wasn't perfect, but most of the time it met my needs.