I use the "Extreme" set (the heaviest) for pull-downs. If you are also using bands for biceps, shoulders, etc., I would recommend the "men's" set, which includes the heaviest one from the women's set as well as the lightest from the "extreme" set. Then, if you need lighter or heavier bands, you could buy the separate ones they offer.
If you are going quite a bit lighter than Cathe on her tapes, you might want to use the "women's" set for biceps, etc.