That is like....your opinion man..
And how is it "more important"? lol
Note i qualified it with 'I think'
But yeah it does come down to opinion. As for 'more important', Street Fighter IV had a much larger impact on gaming than Sonic Adv 2 did. For good or bad it really did give a kick-start to the fighting scene again and bring it back to the masses. Sure it was still doing well before, but SFIV really kicked it into another gear.
In the end though I agree with Barry, ten years is a long, long time for any medium, especially video games. There have been so many important releases that are so different to eachother it's really almost impossible to pick one game that can be declared the best.
Oh wait, Shenmue II... disregard my last paragraph.