Quick distinction, PhotoPass is the photography service they offer, Memory Maker is the unlimited download product.
It really depends on you. Some people are happy with a single family shot in front of the castle to show they were there. Others want lots of pictures. If you did characters alot, it used to be a no brainer. The CM would be in a great spot to get those shots of your party walking up, those first hugs and such, while you still had your bags and stuff. But now they are switching some of the characters to the photos boxes, it's not the same. And I miss the ability to add the borders to the pictures.
If you are going to be there during the holiday season, I would definitely recommend getting Memory Maker. Taking night time shots with the castle or other decorations in the background won't work real well with your camera unless you are schlepping a tripod and such, while PhotoPass usually does a good job of night time shots.
I've usually done well with Memory Maker, but the last few trips it's been included in the AP, so I didn't have to pay extra.