I would like to point out that I've never owned a pitbull (don't ever plan to), and I am not invested in this topic. But I'd like to play devils advocate here in order to promote scientically literate discussion on the matter.

There are many confounding variables that impact studies on dog aggression and reporting of dog attacks.

For instance, this study (PDF warning) found a strong association between deviant criminal behavior and and ownership of high risk 'vicious' dogs. It's important to note the relatively small and localized sample in that study.

To the claim of putbulls being the most vicious breed, this study found that smaller breeds were in fact the most aggressive. A finding which has been replicated by other studies. There are many factors thought to influence this, including the growth factor gene.

Smaller dog attacks are also severely under-reported since they are not as concerning, which further skews the statistics on dog attacks to a very significant degree. Source. Also illustrated in that article is the prevalence of pitbull ownership in specific locations/demographics, which directly impacts the rate of attacks simply due the higher proportion of pitbulls in the given population.

I think it's important to weigh all of the facts, consider the conflicting studies, and address all of the confounding variables that are not controlled for in most of the studies assessing breed-specific violence.

To claim that pitbulls are the most aggressive breed is not a claim you can make with certainty from the scientific literature we have on the subject.

For people more unfamiliar confounding/third variable problems, here is a famous example:

Statistics show that as ice-cream sales rise, so does the rate of violent crime. You should not draw inferences of causation from correlations, but one might arrive at the false conclusion that ice-cream promotes violent behavior.

However, in actually, the third variable influencing both of those statistics is hot weather.

I'm not going to tell anyone what they should believe, but I encourage everyone to remain vigilant in scrutinizing all available scholarly information, avoid engaging in confirmation bias, and do not simply believe other redditors' comments at face value.