Re: How shall we decide our daily diet?

As you said, its all about the individual - some diet approaches do attempt to personalize the diet based on the individual, including the Blood Type Diet and metabolic typing you talk about. Others advocate that a diet rich in raw food (live food) is the only way to go, and many other combinations in between.
I ran into the same "wall" as you, because I started the metabolic typing diet (fast oxidizer, high purine diet) and felt good on it, and then checked into the Blood Type Diet and it turns out that I should be a vegetarian (type A) and avoid most meats and dairy. (I thought I was going to be a blood type B because I felt good on it).
There are some flaws with blood type (like any other diet), and most "oppressors" claim that most of us are not pure bred for one blood type and rather a whole mixture (even though only one type shows up as dominant).

Either way, its all about reading your body responses to food - if you do well with dairy, then you can benefit from it (its all about the quality of dairy (raw), a lot of people think that they are allergic to dairy but its because it has been processed). I had tested numerous foods and diets via EAV and the parasympathetic diet (fast oxidizer) seems to be the best fit for me.

Personally I try to follow Dr Prices advice on diet and food preparation because a great deal of a diet is how you prepare your foods and the quality of the foods (chemical or man-made processed food should be a no-no to everybody).
Mike