If we leave parasite and safety issues aside, what meat is better? With a bit of blood, or really cooked? I think that if you cook it very well, many nutrients will get depleted. How do you eat your meat?
Well, red meat has the advantage of having more nutrients in it, but the more cooked meat is easier to digest for the stomach. However, overcooked meat will also be hard to digest, and will have less nutrients, so it is best to have the meat medium cooked just past the point where stops giving blood.
The more you cook meat (besides burning it), the easier it is for your body to digest actually. Cooking it helps break down the meat and makes the digestive process easier on the body. You kill the natural enzymes in the meat but if you include raw vegetables or a digestive enzyme supplement with the meal, you will get the benefit of the enzymes through those.
You always want to cook your meat thoroughly. Especially if eating traditional store bought meat. Eating raw meat straight from the farmer where it was slaughtered hours before eating is different. Any meat sitting on a grocery store shelf has been slaughtered days/weeks before it even hits the shelf.
It isn't worth getting sick. You can put yourself in the hospital with serious food illnesses by eating undercooked meat.
For me it depends on the cut of meat. If I am having just a basic steak on the BBQ I will go for a medium or medium-well. For something like a prime rib...medium rare.