Depends on what you are aiming for the most.
When moon is in capricorn this brings good luck to any business or workings for it that are started at that time ( workings for money and success) and can bring lots of money, I have found out that moon in cancer can be also good if you would like something you that you want to publish, invest in or start on to bring you success among family, close friends, kids or females and more feminine people (if book is for kids or mostly for females, is involving lots of feminine stuff then maybe moon in cancer could be a good choice). If you want lots of fame and to get popular, then moon in leo.
Moon in gemini, and even virgo also are good overall especially if book is about some popular and trendy stuff, workings at this time are focused on communication especially with moon in gemini, while with virgo mercury energies are more tied towards healing and service to others.
Moon in scorpio would make deep impact on people especially if book is a bit about spiritual stuff...
Moon in aquarius is good for science and science books.
For overall success I would suggest moon in capricorn tho.
Reps of 8,9,10 will all work nicely when it comes to numerology. Also prices with number 9 often attract people to buy things from what I know.