Scrum and Prince2 operate on a completely different level.

As you can see in this post: http://pm.stackexchange.com/questions/1079/can-prince2-and-scrum-work-together

Prince2 is on a PM level and Scrum is on product delivery level, so the position you are in, the environment, organisation and geographical position could be all factors that have an influence on your choice.

One isn't more valuable as the other, if you don't take into account the position you are in.

From my experience I would say (only indicative list, more options are possible):

Choose for Prince2 if you:

 - are geographically positioned outside of USA (although it is growing there as well)
 - want to know about PM, the terminology, the processes, etc.

Choose for Scrum if you:

 - are using Scrum or any derivative like Scrumban