My first priority is for spiders that can web (Black Widows, Corpse Spiders, Harridans) because they really help reduce the risks of trying to capture other critters.
It is very important to get your Spell Mastery as high as you can get it, and given how expensive Tame is at the start, it helps to get promotions or equipment that also helps with the mana cost of tactical spells (Mana of Oceans really, really helps, but it requires level two in Life and Water magic).
Harridan and Hoarders spiders and Umberdroths are probably the best for tanking ... Cave Bears aren't too terrible ... and Great Wolves are always good to have along in any fight, but be careful as GWs are not themselves great at tanking (though self +Enraged with howl, they can get some decent strikes in). Also remember, the +Enraged attack bonus that the GW's howl increases with the GW's level, so its important to try to capture GWs early on (but you may have to wait for wolf packs to grow/level up into a Great Wolf) and bring them with you through many fights to level up.
Stalkers (Plague or normal) are the fastest tactical units I know of and are really good for getting around enemy melee units entirely on the battlefield to take out their archers and ranged spellcasters in the rear.
Silt Skaths aren't to be overlooked, either ... no, not good tanks, not a huge amount of hit points compared with a Giant Harridan or Hoarder spider, but decent movement, decent attack that poisons and a special attack that does triple the normal damage, doesn't trigger a counterattack, and imagine a Great Wolf-boosted attack that is, then, tripled. 
