I've used PornGraph and although I like the fact that the counter is invisible and the stats are very comprehensive, I gave up on them because they are incredibly unreliable. They are up and down constantly and at times the referer logs don't keep an accurate account of the referers. A counter isn't much good if it's not accurate so I've gone back to MasterStats. They have a non image counter so I don't have to worry about nudity on pages where you don't want it and the stats are accurate.