Chihuahuas are pretty aggressive if they feel the need to protect someone or themselves but usually Chihuahuas are pretty gentle and affectionate dogs.
Chihuahuas are also good at sensing when someone is about to come to your door as well and will alert you and they do like to cuddle a lot.
My moms Chihuahua loves to crawl up into the sleeve of my dads jacket and sleep there when he's sleeping in his Recliner.