I think most of us have heard the Brigitte Bardot/Gainsbourg recording of his "Je T'aime Moi Non Plus, but in actuality, I bet most of us only heard the Jane Birkin/Gainsbourg recording. That officially came out in the late 1960s, but it took ten years for the Bardot version to be released on the French/world market. According to legend, the then married (to someone else) Bardot was having an affair with Serge, and they recorded this rather literate song of eros. Gainsbourg wrote the song for her, and it seems he was crushed when Bardot requested that he doesn't release the song, due to the husband's jealousy at the time.
Both versions of the song are excellent, but I have to choose between the two, it will be the Bardot version. For one, Michel Colombier's arrangement is superb. The strings are lush, romantic and feverish. It's the most erotic part of the recording. Bardot and Gainsbourg are very cool in their delivery of the song. Birkin, on the other hand, does the heavy breathing, and the format is more organ/guitar orientated than the Bardot crazed orchestration. Not to make a personal judgment between the two great female icons of the 20th century, but Bardot strikes me as a master of a cool sexuality that is smart and perhaps deadly. Birkin is very much the girl next door - erotically fun and beautiful of course, but perhaps not fully aware of the world - or the seduction techniques of the Gainsbourg method. Bardot is acutely conscious of the 'whole' game.
But like all things that deal with Eros, it is very much part of the listeners take on such a magnificent song and recording. If you have the chance, do compare the two versions, and come to your own conclusion.