that is an easy one - assuming I could only have ONE animal - it would have to be DOGS.
I have had llamas, geese, Indian runner ducks, cats, and all have delightful, different personalities and I so enjoyed my time with all these animals however my dog once saved my life, and dogs are my constant 24/7 companions, so I would not hesitate in saying dogs.
The other animals, although I had strong bonds with the llamas, they were not with me 24/7 like my dogs are.
Can't go past man's best friend!