Brotha Desmond said:
Best archer ever: Gilgamesh.
Considering he doesn't use a bow, I'd say the other badass archer from the Fate series, Archer:
This guy is so badass the word "Gar" had to be invented to descibe him. He can pinpoit shoot moving targets from 2 kilometers away, something people with modern state-of-the-art rifles, bullets and scopes can only do at a still target.
Plus, he breaks Lavoisier's law of Equivalent Exchange by creating magic swords out of thin air, and being able to explode them at will, or use their magic powers, making him able to use a limitless amount of special weapons when most other Servants can only use one.