I'm not going to bother with a poll, because there are too many dog breeds to list. However, I will list some that people often consider aggressive and a couple that I know can be aggressive. I'm going to share my thoughts on some breeds often considered aggressive along with my opinion and what experts say about the breeds. Keep in mind that I am not a dog expert and that I had to look some of this stuff up.
I've noticed that most of these breeds are considered intelligent:
Pit bull- There are actually three kinds of pit bulls (see below). These three breeds are often used for as fighting dogs. This fact adds to their bad reputation. It's a sad situation, because it's really not their fault.
American Pitbull Terrier- This breed is the one most often called a pitbull. For anyone who's actually owned one (and not taken it to fights), it's known for being fiercely loyal and is actually good around children. They are the largest type of pitbull, but they're still definitely considered a medium breed. They're also highly intelligent and thus highly receptive to advanced obedience training.
American Staffordshire Terrier- This breed is actually known to have a better temperament than popular breeds like cocker spaniels, beagles, and collies. They are extremely human-oriented, friendly, and relatively easy to train... hardly a nightmare breed.
Staffordshire bull terrier- This is my favorite type of pitbull, and the one I have the most experience with. Again, they're not aggressive (unless trained for fighting). They are extremely intelligent dogs. They're also known for courage, which makes them protective family dogs.
I strongly believe that the temperament of any pitbull is dependent upon the owner. If they're treated well, they won't hurt anyone. I'd say it's probably best to keep them away from very small children, as they may not appreciate children rough-housing with them too much. Beyond that, they're actually good dogs. However, it's not recommended to get one with any history of fighting and/or abuse unless you REALLY know what you're doing.
German Shepherds- This is another intelligent, strong breed. In fact, they are ranked as the second most intelligent breed behind border collies. It seems that the Germans have created several breeds that are good for herding, and this one is the most well-known. They are often used as police dogs for three reasons: 1) good for advanced training 2) strong and 3) loyal. They're also used as guard dogs for the very same reasons. They're highly intelligent and actually good for children that they know. They're a high-energy breed and should be given lots of exercise (both mental and physical). They also tend to become overprotective if not properly socialized.
Rottweiler- Again, this is a German herding dog, one that's known for being energetic and fiercely protective. Generally they're normally well-behaved around humans, especially if they're given something to do. However, they are especially dangerous if not raised correctly as they are very strong. They are in second place as far as breeds responsible for fatal attacks against humans behind pitbulls (not sure which kind).
Doberman Pinscher- They were bred as guard dogs. They can, however, be trained only to exhibit aggressive behavior on command and are not aggressive towards their owners. They are considered the fifth most intelligent dog breed behind Golden Retrievers, German Shepherds, Poodles, and Border Collies.
Chihuahuas- This is the one that I would most likely not ever own. For one thing, they are not generally friendly around children. As for their behavior problems, I think (as in all cases) that it is because of bad owners who coddle them and let them get away with stuff that they don't tolerate from larger breeds. That's not to say, however, that it is impossible to have a good one. I've known at least two that were very good dogs, except one of them did bark too much.
Dachshund- Although this is one of my favorite breeds, I know that it is not one to raise around small children (as in kindergarten to first grade and below). Dachshunds are impatient and often difficult to train. It's not because they lack intelligence. Rather, it is because they are stubborn. If not raised properly, they will bite people, especially small children. Around people they know and love, however, they are very lovable. They crave lots of attention.
I could list others that people think of as aggressive, but I think I've mentioned the ones most generally considered aggressive as well as two (chihuahuas and dachshunds) that often exhibits aggressive behavior even though people often overlook their bad behavior (which includes growling, loud barking, and biting). The bottom line, in my view, is that there are a few main issues when it comes to dogs. 1) Some people don't know how to raise dogs. 2) Some people breed strong breeds like pitbulls and rottweilers for dog fighting, which causes extremely aggressive behavior. 3) Some people neglect dogs. 4) Some people get the wrong kind of dog for their family/lifestyle. 5) People usually decide to buy a puppy first even though a well-balanced adult dog is often a better choice for a first dog as they can help teach the puppies how to behave properly even if they are different breeds.
All of these problems I listed are caused by humans, not dogs. I was wondering. Does everyone agree with me, that the reasons for aggression in dogs is almost always caused by humans, either through stupidity or outright mistreatment?