There you gave me the help I needed!!!
That was the issue. The Device Introduction 2 comp I nested in another comp (despite the raytraced thing, that was also right, but didnt affect the quality), I didn´t activate in the parent comp the little "sun" to collapse transformations.
When I do that the qulity get´s back to normal and everything is fine! No need of take the button "preserve resolution when nested".
I don´t really know why this works out now to be sincere, but it definitely does just as I expected!
Thank you a lot.