If you're not worried about reaching beyond level 8 Ebon, than NM should be fine. True you get more points for cashing in a HM mode book, and certainly you'll get more points from actual kills and quests whilst completing the book in HM, but then it is harder. It's personal choice then.
If you want to go beyond level 8, then you'll have to complete HM books
http://wiki.guildwars.com/wiki/Hero_handbook shows how many points you'll get for each partially or fully completed book in each mode