I have 3 of them and they're awesome.
https://photos-e.ak.fbcdn.net/photos-ak-snc1/v1184/4/46/630246145/n630246145_1588068_2698.jpg
They have strong amazing personalities and are a pleasure to be around!!! It wasn't hard at all to train them, they were trained within a week on puppy pads (they don't go pee-pee outside as it's too cold for them in the winter + they would be buried under the snow lol)
They are very nice with Josh, and are very cuddly/affectionate. My oldest, Paris, is a little stubborn and is VERY smart. If you piss her off, she will let you know... She pooped INSIDE my husband's shoes once because he didn't want her to take a nap in bed with him... LOL
None of my chihuahua will growl at people or show aggressivity. They are very lovable, they never bit anyone and I don't believe in chihuahua being aggressive. All dogs are animals, if you raise them properly and train them properly they will be amazing.
I suggest you go to a breeder. You will pay a little more, but it's worth it. You are guaranteed a very good quality dog, healthy, great behavior etc. petshop dogs are rarely pure breed and are crossed with other breeds or breed brothers/sisters, creating bad tempers, health issues etc. Also, they can come from puppy mills.
So look around for a good breeder!! Chi's don't require much exercise, just playing fetch with them for 10 min is enough.
Mine are treated like babies, however we are strict with them if they are naughty and don't let them get away with it. They are allowed to sleep in bed with us, they have their own closet for their clothes, and they love home cooked food (salmon, filet mignon, CARROTS!!!)
Good luck!! xx