I'm pretty sensitive to scents, colors, flavor, parabens, glycerin etc. I would never attempt anal sex or even anal play with just saliva, it simply doesn't protect anal tissues well enough. Lube is also necessary when certain times of the month, the "juice" just isn't enough, you've just had a baby and things are very dry, or if for some women in peri-menopause, who just can't make enough natural lubricant every time. It really isn't something a woman has control over.
Not to mention, even the juiciest woman will probably need some lube during a 2 or 3 hour marathon session. (Hell, we run out of spit when it goes that long!)
Our favorite is Sliquid Ride H2O
lube. The Organic Sliquid, from what I have read again and again, won't last long enough for our needs, and we love "The Ride" so much. We rarely even need a second application during anal sex.