Let's forget binary thinking, because the inspiration for travel and guides are not hierarchical, but rather tools for different phases of planning.
Fiction ignites the flame of desire, offering an idealized vision, while guides provide the practical information to realize this vision, much like a medical file gives the steps to treat an illness rather than the inspiration to do so.
A third approach would be to let fiction define the spirit of the trip – for example, dreaming of Renaissance Italy after reading a historical novel – then using guides to build an itinerary that incorporates these specific themes, not just generic tourist attractions.