The Believe in Holiday Magic Fireworks are a limited run, but Disney is also adding a a holiday part to World of Color. Personally if you haven't seen WoC I say go with that, if you have go with the fireworks.
Definitely the fireworks. As posted above, the world of color is always there-year round, where are the holiday fireworks is limited time only. I would do the fireworks.
If you can get back to the parks within a year the fireworks. If it's unlikely you will get back, World of Color. WoC is a great show. The Christmas Fireworks are not the best firework Disneyland has, just special for the season.