You will likely want one that have a good advanced maneuver, so a Wolf or Scorpion would do.
I prefer the bird for mobility. The support options are often a trap, so I don't worry about them. I prefer to use my bird as a flanking pet and extra option for navigating the battlefield quickly.
If you want to help your party more, the wolf is very nice. He'll be limited against flying targets or who are behind hard terrain, but that wolf trip is nice for the party.
If you're campaign is mostly in open air, there is something to be said in favour of the mounts AC.
By level 4, if you take Mature Animal Companion, it's is more or less 1 free stride action if you are using your 3 actions, and if not your mount can either give you great mobility or some attack.
I guess the question is what do you want to do with your AC / why did you decide to get one?
Well, I am new to Pathfinder, my group is running Age of Ashes, and I decided on a Storm Druid, but Druid all but begs you to take a 2nd order. Wild isn't a good complement, as I'd be either casting or fighting at any given time. But then when I started reading all the support benefits, it looked like animal companions are a bad fit for a Storm Druid too.
Something tells me we'll be spending a fair amount of time indoors with Age of Ashes. Still, a Riding Drake would be kind of hilarious.
Deriven's comment on support options being traps help, especially now I read in detail on how those work.
Also I am playing a Tengu, so a wolf is a very flavorful and ecologically appropriate companion. :-D Although a vulture looks interesting too....
Think of your AC as a source of additional actions and damage. It will add a bit of damage pretty often, allow you to help flank, and do other actions like trip or intimidate depending on what you pick. And it can take a hit or few in battle. It's AC is pretty good if you choose nimble.
And make sure not to overlook the ability to pick up a decent weapon using an ancestry feat. A weapon strike here and there does a little extra damage especially with an animal companion and can mix in with your casting.
I like the snake that takes away reactions.
You have missed the obvious one: Vulture
Its support benefit triggers on a hit not a strike. Which means your spell attacks will trigger it.
My thoughts on animals comanions are here.
If you're campaign is mostly in open air, there is something to be said in favour of the mounts AC.
By level 4, if you take Mature Animal Companion, it's is more or less 1 free stride action if you are using your 3 actions, and if not your mount can either give you great mobility or some attack.
I guess the question is what do you want to do with your AC / why did you decide to get one?
A weakness with a lot of four legged animal companions is a lack of climb speed, so when your party needs to climb up or down a wall, cliff face, etc. your four legged buddy can be a bit of a liability.
This is not a common, but when it happens, it can be annoying. Especially for a large animal companion, like a mature horse.
Just some food for thought on benefits and drawbacks of some types of animal companions.
If you're campaign is mostly in open air, there is something to be said in favour of the mounts AC.
By level 4, if you take Mature Animal Companion, it's is more or less 1 free stride action if you are using your 3 actions, and if not your mount can either give you great mobility or some attack.
I guess the question is what do you want to do with your AC / why did you decide to get one?
A weakness with a lot of four legged animal companions is a lack of climb speed, so when your party needs to climb up or down a wall, cliff face, etc. your four legged buddy can be a bit of a liability.
This is not a common, but when it happens, it can be annoying. Especially for a large animal companion, like a mature horse.
Just some food for thought on benefits and drawbacks of some types of animal companions.
Pet Cache can help get your heavy warhorse into that dungeon.