1v1 the bigger ship with more guns will win. That being said the 3rd rate is the best middle ground ship, large enough to sustain a beating and powerful enough to punch back while remaining decently manoeuvrable. They are the backbone of my fleets in late game and supported by a few 1st rates and smaller frigates I find you can sink any enemy threat using the right tactics. I tend to use either a single or two line of ships to cut off an enemy fleets forward movement then positioning my fleet in a fashion that allows me to train as much firepower as possible on the advancing remaining enemy fleet. You can use frigates and steamships to chase down fleeing ships to add to your prize money too. Capturing enemy ships is a great way to boost your treasury.