If you're counting gas giants on the same scale, we should be small or perhaps the low end of medium.
In terms of just rock worlds, low end of Large or high end of medium.
This one would be the high end of huge for rock:
http://www.cnn.com/2004/TECH/space/0...net/index.html
Population scales are completely out of proportion; on a gas giant like Jupiter, you could have two trillion people at Earth's population density. Also presuming that you don't take advantage of living at different altitudes for gobs more available space.