It's all about how you raise them. Main problem are the people who get them because they're "bred to fight" and "look gangsta". They don't give a shit about training them, and that's how you get loads of bad behaved Pitbulls. It's really sad.
My dogs half pit half German Shepard and I can confirm this,she really loves to play tug of war and is super strong but as soon as you hand the rope to a child she instantly stops pulling as hard and will even let the kids win.
Small dogs usually have a Napoleon complex, that's why they're such little shits.
My grandma has a Yorkie and she's lovely though. Even with Napoleon complex dogs, you can just eliminate most problems by raising them right.
The Napoleon complex does not exist in animals! That is a human only trait. Small dogs are bred for size and cuteness, behavior and sociability are not even an afterthought. Security dogs are bred for loyalty and the ability to listen, anger or disobedience are quickly culled. Two bad traits that are inheritable are anger and shyness, and both are tolerated for small dogs. It's not a complex, it's bad breeding.
Or you know...it might just be how the dog is raised. Aggressive and friendly dogs come in all shapes and sizes. Breeding can only tell you so much. The dog's experiences and training are where it really counts.
My grandma has a Yorkie and she's lovely though. Even with Napoleon complex dogs, you can just eliminate most problems by raising them right.