1) Options sorted by druid-lvling-speed, from fastest to slowest:
- Farm instances as high lvl as your druid can enter with any of your high lvl chars.
- Solo a bunch of quests
- Make 2 chars and do a bunch of quests
- Have your high-lvl help you with quests

2) Probably Demonology, even for lvl 10-49 it'll be nice that your voidwalker isn't constantly losing aggro, and from 50+ it simply owns.