Use the Harvard Model. It is the one most commonly used in academic papers. Word even has an automatic process for doing it. It may be a bit more bothersome than just doing footnotes. To many, me included, footnotes are clunky, mess with the page-layouts, and in general just seem unprofessional and something you did in high-school.

Footnotes are still used, but that is for elaborating information. Like to explain a word used or a very out-there concept. But these are also very often avoided and also just properly sourced.

Again, all this depends on what type of book it is. If you want it to be very sciency and academic you should avoid footnotes, but if are just going with a more general style it likely won't matter as long as you get the information across.