Well, I guess it`s a combination of both really. Caz relying just on either one is not a good thing. If u tend to memorize only, then yr note reading will turn out to be very poor, and so will yr sight playing. Sight playing is very imp. to a pianist. On the other hand, if u just look at the book, u might overlook alot of intricate details...and occassionally, even Musicality.
This is what I suggest u do: Try to feel yr fingers, dun need to look at them to know that they`re curved or positioned properly. Look at the book, and try not to stop. But once u come across any problems..say slowing down, or unfamiliar notes, then it`s good to memorize just the problematic part. After that few bars or so, continue looking at the book.
This is just a practice strategy..u can do it yr own way, as long as u feel comfortable with it. BUT, if yr talking abt. playing in a recital...then it`s a must to memorize!
