Maybe a Woolly Mammoth or Dakotaraptor.
That's a hard question, either Microraptor or Yutyrannus.
Microraptor because I could do falconry with it! Kinda like what was suggested for this mod.
And Yutyrannus because.... well... its like a T.rex except its smaller and not as dangerous.
And I could cuddle with both!
Just felt like I should clarify, Yutyrannus was not much smaller than T.rex. It was only 3 meters shorter than T.rex, meaning the animal was about 9 meters long, while Tyrannosaurus is about 12.