The best food for humans would be vegetarian food. If you eat green vegetables and fruits your digestive system readily accepts it, and it easily gets digested. There are many advantages in eating vegetables. Your blood becomes purified, your skin becomes really healthy. You start feeling fresh and your immune system improves. This to say your vision improves and a lot of other advantages.
But if you are an athlete or doing heavy activity non veg is the best. But non veg should also be eaten occasionally and not always. It is difficult for you to digest it and sometimes very acidic due to high pH level in meat.