For clear speed, it'll probably be Wind Druid. Decrepify isn't hard to get on merc and it increases nado damage, which goes through enemies and can also hit them more than once. Hurricane deals OK damage too and hits everything non cold immune in its radius.
Fire druid blows because most of hell is fire immune and the spells are on a timer. For actual DPS, fissure is actually not bad and is a lot like blizzard.
Fireclaw bear can't teleport, is melee, and you also have the fire immune problem.
Fury druid has no AOE, can't teleport
Rabies druid is alright for certain areas but has no decent way of removing poison immunity.
Summon druid is trash, I bet even concentrate barb kills faster.
You could combine some of these builds like
Shaman - max fissure, synergies, bear, rest of points into oak sage or heart of the wolverine.
Rabies/fury wolf - max rabies, synergy, and fury. Use eth tombreaver for physical damage and rabies for AOE. Put enough points into the passives to make the build work.
But yeah my money is on the Wind Druid.