Grettings! What is the best to render and print a book A3 portrait of mandalas ?

Opacities might lead to rasterization. So maybe you'd want to check the transparency flattening settings. If you also have pixel based effects applied, check the document raster effects resolution. And then check the image compression in your PDF.

It's absolutely not clear what you mean. You have to provide actual info about the export settings, screenshots and so on. Just saying that something loses quality is not really useful when we don't know how the artwork is supposed to look vs. it actually looks and what settings you use.

Mylenium