u/Aggravating_Laugh_48

I'm a new learner, about three months in. One of the songs I took up a few weeks ago is Siubhan Ni Dhuibhir, from the book Traditional Airs of Ireland. In the book, the song is in the key of D (first pic).

This morning, I was poking around the Tony Dixon music website tutorials for the D whistle and came across the same song, but in the key of G (second pic).

I know both keys are doable with my high D whistle, but it's not a whistle question I have.

How do I know which version I should be learning? Or does it even matter? Should I learn both? Is it just personal preference based on sound? TIA for any insight!

Same song, same whistle, different keys?