Which is the best way to memorize score?
Memorize the fingering/how it is played; or have a visual memory of the score in mind? 
Use as many senses as possible for memorizing. Mindless repetition is OK, but there are so many other senses that can help in the learning process, might as well use them in an active and fun manner. You will find that you may personally excel in one way over another. Similarly, you may find that the characteristics of certain pieces will reveal themselves in one way over another to allow for easier/simplier memorization.
LOOK at the notes on the page, LOOK at the shape of the chords on the page, LOOK at the fingerings you have decided upon, LOOK at the position of your hands, FEEL the shape of your hands, FEEL the keys in between and under your fingers, LISTEN to the intervals and the voices, SING the voices, TAP the rhythms of a particular measure on your lap, SPEAK the fingerings outloud as you play, SPEAK the notes as you play, SPEAK the key of the chords as you reach them, SPEAK the type of rests there are in each measure of music, WRITE a particular run worth of fingering down on scrap paper, WRITE a particularly complex chord down on blank staff paper...
Once you start to remember the piece, you will find that there are some pieces that you might be able to re-write completely onto blank staff paper note for note, fingering for fingering, because you maintain the ability to SEE the page (for me, a piece like this is the Rach prelude Op23No5). Then there are other pieces that you might not SEE as well, but their secret is in how they FEEL in the hands (for me, this is Ravel's Sonatine).
Try to engage as many senses and region of the brain, and you will find that your knowledge of the piece will be much more secure.
Good luck!