Well, The Elfen Lied anime is totally more violent than the fist of The North star anime, cause Fist of The North Star totally censored the violence from the manga while Elfen Lied dint.
But i must say, having read both the original manga of Elfen Lied and the one for Fist of The North Star, i think Fist of the North Star is more violent in their original medias. Theres just something about seeing peoples body parts explode and their guts or brains or whatever falling out that is......... very violent. And also, the many many bandits in that manga are just ruthless. Not to say that Elfen Lied isn't, the stuff that happens later on in the manga is far more violent than anything that happens in the anime, its just not as gory as Fist Of The North Star.