I wouldn't trade any of them for a Mabari.
No matter how useful or how much I like/dislike any of the party members.
I loved having a Mabari in the first game, and it was nice to be able to have one in the second that, whilst not an actual party member, was still a part of my character's life in a similar way to the first game.
I'd happily have taken the option again for a mabari if its implimentation was similar to DA2 - a summon. Alternatively, if the dog tagged along similar to NPC pary members like Stroud etc, and not being able to micro-manage them.
Despite already saying that I loved having a mabari in Origins, he didn't really have any significance outside of the Human Noble origin beyond being a mabari that chose to go with you if you saved him.
Human Noble at least established the dog as being part of your character's life as a Cousland thus making it more significant than the other instances/circumstances of getting a dog in Origins.