I've also used Page Plus since the PPlus 5 days and have been delighted with every update and enhancement. I edit, design and publish books of every description and PPlus X9 does all I want in terms of input, processing, outputs, and fantastic Community support. I work with other designers, for whom InDesign is king, but they learned it in college: I never had time to do that, and the Adobe suite is, for me, well described by Stevekelly, above.
However, Serif won't maintain X9 except as a legacy programme. I have great confidence in the Serif/Affinity developers and I accept their reasoning for a complete rework of their publishing software. I'm sure that Affinity Publisher will (after early problems) be a superb programme, but it needs at the very least to provide the facilities that we enjoy in X9, including .docx inputs, BookPlus, and ideally, eReader outputs. It's good to see that .docx input is now on the developers' list of requirements.
PPX9 wasn't very stable when first launched and I had to revert to PPX8 for 12-18 months. I guess the same thing will happen with APublisher. I'll examine the Beta releases, and will move across when the commercial release is stable enough not to loose a book.