You could earn a degree on the classifications and attributes of different sailing ships. Sloops, frigates, ships of the line, fifth rates, sixth rates, etc, etc.
What I want to now is, is there a particular type of vessel that pirates were more likely to use? How did they get their hands on them? Was speed more in their interest than strength? What ships were used by the most successful/infamous pirates?
Thanks for your help.
I recently answered a similar question HERE.
The most likely vessel for pirates to use (and I'm confining my answer to the 'golden age' here) was generally the most readily available in whatever region they were in. That's a facile answer, but nonetheless accurate, broadly speaking.
Speed and strength were both important, but in variable degrees depending on their likely prey. So, in the Caribbean where the most common trading vessels were small, fast, poorly-armed sloops, the pirates needed vessels fast enough to catch the sloops, and strength was less of an issue because the addition of even a couple of guns enabled them to out-gun most of the vessels they were likely to come across. Of course, the prevalence of sloops as trading vessels also made them the most easy to come by, and so in the Caribbean the most common vessels used by pirates seem to have been sloops.
This has led a lot of historians to state that sloops were the most common vessels used by pirates, without consideration to what they were using in other regions of the world. At various times, and particularly after the fall of Nassau as a pirate haven in early 1718, Anglo-American pirates spread out and large numbers of them headed for the African coasts and the Indian Ocean. In those waters there were many fewer sloops, which affected both what was available for the pirates to use and what their common prey was likely to be. The large merchantmen and slavers that were found on the African coasts were generally not so nimble as the trading sloops of the Caribbean, and often much bigger and better armed, so for the pirates speed became less of a necessity than strength. The result was that among pirate on the African coast (Bart Roberts, Edward England etc) sloops were less common and larger square-rigged ships with powerful banks of larger guns were much more common, sometimes with an accompanying sloop to act as a 'tender' or scouting vessel. In the Indian Ocean the same was true. The prime targets there were the large East-Indiamen, which were often frighteningly well-armed, and so too the pirates preferred larger and more formidable ships for themselves.
Given such regional disparity, it's difficult to quantify exactly what was the most common or preferred type of pirate vessel, I think you'd have to be more specific in the question.