I would have to say get a puppy that way Esme and the puppy can bond easier. I once made a mistake and brought an adult home and she hated my chihuahua attacked her twice and I found her a home after that. Sometimes when they are older and haven't had a stable home they will fight for your attention and I don't think you would want that to happen. when I brought Adina home my chihuahua wouldn't like her but she never has attacked her maybe the fact that she was a baby had something to do with it and now that Adina is older Chiquita will try to play with her but Adina is too fast for her. Same when I got Whisper Adina didn't attack her but would just ignore her for about 2 weeks now they are best buds. I think you should stick to a puppy maybe under 6 months old because at 1 year old some are not as playful and under 6 months they almost are all playful.
Smiles,
Myra