In my experience, Druid is tournament-worthy. But building a resilient Druid spellbook is very tricky. As soon as I got my hands on the DvN expansion I've been toying with her because I really love her mechanichs and I have tried lots of different builds (aggressive, turtle, miriad of plants, solo, animals&plants) and here are the builds I've tried which, in my opinion, have a chance of performing well in a high level environment:
1. Very aggro Druid with plants. Plants have a very good cost/attack ratio but their survivability is quite low, so they can really shine in a fast build which aims for a quick game. Vine sappers are extremely good against spawnpoints and, combined with rouse the beast and vine spreading, can start the fight very quickly. In the meanwhile, the mage can actually go into melee as her lifebond makes her quite durable. I usually start Vine tree+double move to NC (10), then double vine+Raptor vine+Rouse the beast+double move towards the opponent (
, followed by several rounds of Vine sapper+Rouse the beast (I play 5 copies of it) to take down any spawnpoint.
2. Mid range Druid with animals. Just imagine you are playing a regular Beastmaster but with very good abilities and 10 channeling after deploying Vine tree. Use the spawnpoint for 1-2 Raptor vines and 3-4 Tanglevines (maybe another couple of vines), but do not rely on it to spam plants as they can be killed quite quickly. Instead, use animals as your main force, buffed with the awesome nature enchantments. I usually start Vine tree+Mana flower (5), Timber wolf+Mana flower (2), Enchanter's ring+any face down enchantment (11), grizzly+enchantment (5).
3. Solo Druid. I developed this spellbook while Charmyna was working on his BB, using Battle forge to stack some armour and Veteran's belt while the mage spends her mana and actions on enchantments and Dissolving/corroding enemy's armour. At some point, when I have saved some mana, I will start throwing Hurl rocks with elemental wand until I get the kill. As I said, it plays extremely similar to Charmyna's BB. I tried it in some games and it is undefeated yet (though I need more testing).
I have little experience with the Necro, but I think he is a nice contender at tier 2 (tier 1 is Wizard).
Hope this helps!