Well, I've never actually had liver before. Something about it just really skeeves me out for some reason. But for some reason I think I would feel better about eating it if it were made into something, with spices and salt and stuff, lol!!
Pate was how I got past my skeeve factor about liver. From there I have branched out to other offal such as heart, tongue, and brains. Offal has a much higher nutrient content than just plain muscle meat.
Liver has been called "Nature's Multivitamin".
I agree with Cori that poultry livers are a good place to start. Goose is awesome. Beef liver has a stronger flavor. My personal favorites are lamb and calf liver. Younger critters have milder tasting livers it seems.
Jeff Volek & Steve Phinney are experts in the field of low carb, especially to the ketogenice level. I suggest checking out their work, as they prescribe ketogenic diets and have specifically targeted how to prevent mineral/nutrient deficiency through diet.