I have a standard Chihuahua that is a little over 5 pounds. Before we adopted her, I never would have considered a chihuahua as a pet. I thought they were very high strung and yappy.
Pumpkin is my little angel, though. She is very quiet and well-behaved. She's good with everyone and will sit in your lap all day if you let her.
If you want to avoid a yappy dog (and this goes for ANY breed), you really need to observe how the dog interacts with people and other animals. You'll probably have a good feel for its personality within an hour or two.
BTW: here are pictures of my little "rat":
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