They must be converted by the body into active estrogens. It is also the most widely prescribed hormone in the world. A combination of E1,E2 and E3 called Triple Estrogen or Tri-Est,has been available for many years. It's proponents claim it is the most natural way to take estrogen. Triple estrogen is difficult to get.
Estrone is easy to get.
Most of the prescription estrogens when taken by mouth are converted in your GI tract and end up predominantly as estrone. If you consider natural, getting your estrogen levels up to where they were before menopause then estradiol is your natural estrogen. The transdermal patches, vaginal rings and estradiol creams provide pre-menopausal levels of estradiol. If you desire a natural estrogen that is the least likely to cause cancer then estriol may be right. Tri-Est contains mostly estriol.