I've sailed about every ship class in POTCO and I have fought all the ship classes in POTCO.
Against regular NPC ships ranging from Ferret to the rare Juggys, a light sloop can sink them with ease if you know what you are doing. So comparing ships which is best against regular NPC ships, each different ship class can do the job with ease if you know what you are doing.
Against hunters or warships, it gets a bit more difficult f you are alone. Against NPC ships... even hunters/warships, you can avoid getting hit by their broadsides by stop and go. In Galleons case however, especially if you are copperhead, its like basil said early in the thread Big moving targets because you will get hit most of the time. With 0 skill points on windcatcher, you sail at 8 knot and with full windcatcher, you go 10. Take off 1 if you are copperhead and you are like a turtle. In my opinion that's really bad because you will be getting hit like every time the other ship attacks.
NPC ships are just doing what the computer tells them to do so they aren't really thinking whats gonna happen. The real test in ships comes in SvS where people with a brain sail(well most of them
). My advice would be, unless you are just using as a big joke, keep it away from svs because you will be an easy target for another player who is aiming at you and a sailor who is gonna be circling you around before you start to move your ship.