In my estimation, The Beatles' version of "Baby It's You" was a major improvement on the original. The latter, performed by the Shirelles, isn't without moments of recommendation, such as the rumbling, hollowed-out rhythm during the pre-verse "sha-la-las" or the weirdly electro keyboard/organ solo. But to its detriment, the vocals lack the sort of color and vitality that John, Paul, and George's have. The comparison isn't even close, actually. And the dominant rhythm, the one that anchors the verses, has a thin, almost jabbing quality that keeps the song too grounded. Overall, the Shirelles' version just doesn't feel as fully formed as the Beatles'.
(If the embedding is disabled, go here).