Generally, you'll want to pick worlds that are geographically located nearby to your location. So, if you are in the US, you will find your ping will most likely be lower on US worlds.
You can check what the ping of a world is via the command prompt on your computer. The command you would want to execute is "ping oldschool<worldno>.runescape.com", where <worldno> is the world number after subtracting 300 (so, World 301 is oldschool1, World 450 is oldschool150, and so on). The lower the number reported, the better the ping. Try a few worlds in different locations and you might find some that are better than what you are currently getting.