I don't really have a lot of hands on experience with the druid other than some theory crafting, but from what I can see I'm figuring your Warlock will be able to handle more types of opponents. He just seems to have a better tool box to me in the books you posted, while the druid is just really straight forward without a lot of wiggle room. Not to mention an opposing Warlock or fire wizard could spell doom for her.
This answer is based purely on the books posted. With tweaks you could strengthen the druid if you wanted to play her instead. To start with I would include an answer for if my opponent is playing with fire, such as grizzly or galador. I would also include more dissolves and/or acid orbs (take advantage of the water training). Some crowd control would be nice too, maybe sleep or night shade orchid.
If you do play the Warlock, I would put in cloak of shadows. It is a huge help against wizards which are very powerful foes. It protects you from both wizard's tower and teleports into pit traps.