An Into The Dead 2 Best Dog Companions post with information to help make a better choice when choosing a companion. You will be able to choose a pet once reaching stage 8.
For more check out the Into The Dead 2 Wiki with guides and more
Crossbread – A basic dog with any buffs accept being able to attack zombies which will conserve ammo.
Border Collie – While having this dog equipped you will find more ammo crates for more bullets. This can be a big help when it comes to always having enough bullets
German Shepherd – Will save you from death once per run. Not dying on the first mistake can be a big help when it comes to traveling far. This may be the best dog and can help with less level loads.
Bullmastiff – Will attack zombies more than the other dogs. This could be close to the Border Collie which offers more ammo, but this dog wont attack as fast as a trigger finger
Into The Dead 2 Best Dog Companions Poll
The poll below will help give a better understanding of what might be a better option thats not so obvious.