This is my ranking of piracy ships, I've built them all for that purpose in some time in my delinquency career on elite (in exception of the Cobra MK4) and the explaination for the ranks is like this:
Prime Privateer:
This ships are the best for any pirate, you have good firepower and plenty of diversity to install all the tools to get that loot that don't belong to you... yet, being well built this ships it'll make you a name in the blackmarkets of the galaxy.
Dread Buccaneer:
This ships are almost as good as the upper tier but all lacks in some way or another, some of them doesn't have enough room for cargo, others have too many hardpoints to allocate the tools for piracy and also hardpoints to defend the loot.
Rookie Rapscallion:
This ships looks like they will be very good at piracy only to flop in the heat of the heist, too many weapons and too small cargo like the previous ones but this ones could be of use in other pirates activities such as megaships cargo extractions.
Silly Scallywag:
This are the ships that usually get robed by the others tiers, they slow, dullish and easily get overrun for even the novice pirates, some silly pirates build their pirate ship in them to be disguised.
Boat Boys:
This ships are too small to be a good pirate, usually are the first ship that a pirate has and then forget when he gets enough loot to buy something better, the Federal Assaultship is here because of its limited internal modules. And the alien ship is here because I've never seen one of them smuggling to the blackmarket.