Spirit Animals are at least +1. I'm not sure if the Avenger Sword Spider is even that good and the other Avenger forms are wimpy with the exception of special purpose uses (ex Salamander vs the Guardians in Firkragg's). I think the Greater Werewolf is +2 though.
Still, the biggest advantage is that the Totemic Druid can use the animals WHILE casting spells. I would love to see an item that enabled an Avenger or Shapeshifter to cast while shifted.
Off the topic, but still on druids, just killed Firkragg with my Avenger/Fighter (imported from BG1 to avoid the Str/Con penalties). 2 Fire Elementals and Bottle Efreeti for Support, Stone Skin, 5xArmor of Faith, Protection from Fire, Sword Spider with 6 attacks (fighter bonus and boots), 25 Dex (potions of Mind Focussing), 24 Str (Potion of Storm Giant)...
The fight took less time than the preparation