Both are usually right around $40 per person...
The Christmas Party is about 5-6 hours long in the MK, is most rides and some special shows. They have "snow" on Main Street much like they have at The Osborne Family Lights at MGM. There are stands to get hot chocolate and cookies, and there are stands to have a picture taken. The "proof print" is complimentary and you can order more if you would like. This is a special admission event that requires this ticket to attend.
The Candlelight Processional package includes dinner at restaurants, and the price of the package is dependant on the tier of the restaurant. You will need admission into EPCOT to use the package, but your regular daily admission is all you need, no special ticket. Depending on the times you've selected (for which order you do things) you have your meal and attend the show at the American Gardens theater across from the American Adventure. There is a celebrity narrator who tells the story of Christmas woven into a 450 voice choir and full orchestra with a bell choir and the Voices of Liberty singers.
Both are fun, I would enjoy the Candlelight Processional more - just a personal preference.
