Spending 10mins googling would probably help more on understanding the difference, for my 2 pennies Prince2 is more about the process of project management, ie. what steps to follow in certain circumstances, suggested templates etc… I tend to think of it more as 'project management by numbers' It's definitely falling out of favour at the moment, I think the industry is going through a bit of a backlash against ridiculous over documentation and specialisation.
Agile (& Lean) are more about how you go about doing things, building self managing teams, collaborative leadership etc…
Personally I've taken 3 OGC courses over the years – Prince2, MSP & MoR. I'd also recommend some of the ITIL qualifications.
I'm currently running projects using SCRUM (not got any formal qualifications in it) – 3 months in and it's working well so far.
If I was recruiting a PM I would expect to see at least some professional qualifications no matter how much experience they have.
I reckon the most useful skill or training would be some form of jedi mind control though…..