Why not use both? If I am in an outdoor zone and able to use a mount, or in a non chain pulling group, or I am camping a specific named and only killing a few mobs... then I go for 2hb. If I am in an indoor zone, or in a high paced constant pull mob in camp every second group, or I am chain pulling with my box bard... then I go for Tome.
If you are in a consistent killing group, one that does not take breaks and chain kills, than it is a much better choice to use the book to maintain your mana pool. If your group is casually doing its thing where you will have time to med up at some point and or use Monster Summoning, 2 hander will be the better route as it is more DMG. Most importantly it varies mage per mage. If you are not having mana issues using 2hander, use it. If you are, use the Tome.
I use book on raids and a shield when I solo because of root breaking caused by proc on book. I keep epic 2.5 equipped at all times. This coming from a necromancer's perspective.
