The 1Plus2 generally excels in most areas and I don't think it does a bad job with female vocals. The Sui for me can be a tad hot in this area due to how energetic the IEM is. With female vocals with lots of energy or a poorly mastered track things can be problematic. But this is more so based on how the track was mastered in my experience. The 1Plus2 will be the better all-arounder. But I enjoy both and will keep both :).
Although if you are mainly concerned with vocals have you considered the Fit Ear 334s? That may be what you are after if that is what you mainly have in mind. Just note the bass decay is noticeably slower than the 8as and in that I found it to be a problem (too slow) and felt congested with bass.