I sing, I don't play any instrument - so I tend only to hear the beat of the chords rather then what they are. For me it is the melody - especially the profile of the melody. What I tend to learn is the relative intervals between the notes of the melody - and then take it from there. (While convenient for me - since I can then "transpose" up or down on the fly as I just follow the profile I've learned- it does bug other people because it means I quite frequently start songs in a random key - while they have learned it in a specific key. Therefore I perefer to let others start)