Sorry if this is too noob a question, but if a druid takes the animal domain as his nature bond, and gets Summon Companion that stays until dismissed, does that mean the druid essentially can have an animal companion picked from the Summon Nature's Ally list that's "permanent" until dismissed? Or does it only stay for the duration of that spell OR is dismissed?
The other way seems like it makes getting a normal animal companion pointless, since with Summon Companion you can "upgrade" your choice all the time and still have your animal around with you all the time. Am I making sense?
Generally speaking, the companion you get from the Animal domain will be weaker than what you could get as a normal animal companion. E.g. at level 4, you'll have a wolf instead of a dire bat, at level 7 you'll have a dire bat instead of a dire wolf, and at level 13 you'll have a dire wolf instead of a dire bear.
Don't forget that a true animal companion gets bonus HD, bonus BAB, bonus Saves, bonus to STR and CON, bonus to AC, and extra abilities like Link, Share Spells, Devotion, Evasion, Improved Evasion, and Multi-attack.
Then again, it sure would be handy to summon whatever companion you want for the day. Maybe a wolf in the forest, an eagle on the prairie, a bat underground, and a shark in the ocean. Hard to do that with a true animal companion...
And the Domain grants other stuff above and beyond the companion.