Well, the biggest factor is your location. Our servers are in the Netherlands. Sometimes our respective ISPs don’t choose the optimum route between each other and that makes downloads slow. The quality is ever-changing, and all we can do is try to route around slow connections. This is why we have created alternate routes all over the world. Not the best solution, but it helps.
Our default proxy is CDN77, which should be automatically routing the traffic from an endpoint close to you. CDN77 is a CDN (Content Distribution Network) provider and they have many endpoints around the world to help speed the internet for companies like us. This proxy should be good for most of our users.