No experience with the Giant, but I love IsoSpeed. As I age, I find comfort climbing the priority list.
I considered the Checkpoint as well. It's a great bike. I suggest riding both and getting what
you prefer, because you'll be in the saddle. For me, I'm partial to Trek because my LBS sells them and I get great service there.
EDIT: The reason I did not go with the Checkpoint was I do more road riding (> 98%). If I did more gravel, I would own one.
