I would like to know what is the better way to dress sushi and sashimi. What I am looking for is how it was thought to be eaten and what are the ways a sushi piece is supposed to be dressed with soy sauce and wasabi to obtain a balanced taste!
I remain extremely skeptical that there is a right or wrong way to dress, pick up, eat, or otherwise deal with sushi. A Google search for "is there a right way to eat sushi" turns up hundreds of pages, many with contradictory information.
If there is a "right" way, it's most certainly dictated by the locale or restaurant you're in or the people you're with. My advice is to do whatever you want, particularly if you're paying for the meal. If you're a guest, follow the lead of your hosts. But don't sweat it. Enjoy it!
UPDATE since the original question has been edited...
what is the better way to dress sushi and sashimi.
"Better" is still difficult to define for everyone, and will vary by each person's taste. Something that "enhances" flavors for me may be completely unacceptable to you, and vice-versa. There's no accounting for taste! But since you made an effort to clarify your question, I am updating my answer accordingly.
Sometimes the "better" dressing is none at all. This is particularly true for Unagi or others that have some kind of sauce already applied (though I know some people who dip Unagi in soy sauce and claim it is great). I have a daughter with soy allergy, so she cannot use soy sauce at all and doesn't like wasabi. She enjoys eating salmon and tuna nigiri pieces completely plain. I've tried it myself, and with good, fresh fish it is really good.
I have heard of people dipping the pickled ginger in the soy sauce and using that as a kind of "brush" to gently apply soy sauce to the topping. That may be "better" if you are adept with chopsticks and enjoy pickled ginger along with soy.
Some people dip only the topping into the soy sauce, to avoid getting the rice saturated. This is a little easier to do if you use your fingers to pick up the sushi pieces (and according to some accounts this is perfectly acceptable for sushi) (but not sashimi).
Some people mix wasabi (sometimes, copious amounts) in with the soy sauce and dip the sushi into that mixture. Some suggest that soy + wasabi should be reserved for sashimi only.
Soy sauce, wasabi and grated ginger.
If you are eating sashimi, you can mix a bit of wasabi and/or ginger with the soy sauce. If you are eating nigiris, the chef probably put wasabi in it, so you may not need to put more.
But remember that the point of eating sashimi and nigirizushi is to feel the taste and the texture of the fish and the rice. So be really gentle when dipping the fish, or you will kill all the taste. Only a touching one corner of the fish should be enough... and for the nigiri, don't touch with the rice, or it will get damp.