Like everyone said....talk to your doctor. Of the 3 listed, premarin is derived from pregnant mare's urine, so lottsa horsies in stalls, being pregnant, confined, and peeing for the world's women.....The second, prognova is a precursor to natural estradiol, and is broken down by the liver into that compound.......and estrofem is 17-beta-estradiol, which is bioidentical to the hormones produced in the human body, but is extracted from plants.
Your doctor should help you make a good choice.
Bev