nutrient density is the amount of nutrients you get per kg. Water would have a nutrient density of 0. You could argue that a product's water content is an inverse measure of nutrient density. Bone broth is extremely UN- "nutrient dense". So therefor it is liver.
Although I would eliminate liver from my diet before bone broth.
Liver is more nutrient dense, to be sure, but that doesn't mean you should choose liver over broth. I think both are important, for different reasons.
If pressed: liver is "better"
But really it depends on the rest of your diet. If you're already getting what liver offers, bone broth could have a greater impact on your health and quality of life.
Essentially I think you'll get the most profit from consuming liver, else you'll be losing all the extraordinary fat solvent vitamins unless obviously you utilize the fat from your stock, admittingly I dispose of the majority of it.
Liver definitely has more nutritional density than bone broth. Liver is chock full of vitamins, minerals and nutrients while bone broth is mostly water with a low concentration of minerals.
One isn't necessarily better than the other though, bone broth is better if you're dehydrated and liver would be better if you were otherwise lacking minerals/vitamins in your diet. Too much liver could be bad too, specifically because of the vitamin A.