Both. Brian Wilson does a pretty good job singing on his 2004 version, if a bit creaky, and when he is overreaching, his backing band fills in for him.
And get the Purple Chick bootleg of the Beach Boys version. They take liberties with some of the arrangements to mimic Wilson's 2004 version as best as they can, but of all the bootlegs I've heard, this one sounds the most "complete".