Although I really like cutting my sword in to anybody that crosses my path, my old pirate hearts remains claimed by the sea - but not as much NPC fighting, as SvS.
Depending on where you are, Privateering can easily be the most action-packed part of the game. There are times when it's slow and easy, and other times when it's just an all-out chaotic battle. I find it hard to find a more diverse experience anywhere else in game, aside from the events run by my guild and friends.
I guess I'm kind of biased on the subject, because I used to be an avid Privateer myself back in the day. (Or maybe it's because of my super shiny Commodore Badge
) Either way, I'm sticking with the seas on this one.