i think kisame is probably up there....maybe the top 3 or so. Not that we'll ever know for sure. Its very unlikely kishimoto will actually go into the mist swordsman story. It was just something to make kisame seem like a big shot i think. More of a detail to his back story rather then a plot line on its own. As such, i think we might have to accept raiga as an official swordsman too, now that he's been shown as one in the fillers.