Both: Six of one, half a dozen of the other.

Susan: If they don't fit right, I'll give 'em to my brother.

Both: But all the same, don't we have fun?
Half a dozen of the other, six of one.

(not sure where the next line fits in:)

Gordon: Not much money to spend ...

(Somewhere in the song, Susan is admiring some garment, and Gordon sings that he thinks she'd look just perfect in it for Halloween. I think the last chorus goes:)

Both: Six of one, half a dozen of the other.

Gordon: If I don't get this, I'll never have another.

Both: But all the same, don't we have fun?
Half a dozen of the other ...
Six of one!