Estradiol is the best feminizing agent. It feminizes every part of the body and is the same hormone found in cis women; it seems to work well for them. When it fails to cause good feminization, it is usually because the dosage is too low. High doses may cause thrombosis in people who are already susceptible to it, but the risk is near zero for an otherwise healthy adult under 40. A bigger (and often overlooked) health threat from estradiol is candidiasis, which can be prevented by avoiding yeasty and sweet foods, taking probiotics, and maintaining a healthy immune system. Other estrogens have many more health risks and have not been shown to be more effective than a sufficient dose of estradiol.
I warn against spironolactone because it makes skin severely rough and dry and age rapidly - a very upsetting side effect. It can also cause fast/irregular heartbeats, dehydration, excessive urination (including overnight), fatigue, and hyperkalemia. It is also less effective at suppressing testosterone production when compared to certain other androgen blockers/anti androgens. Furthermore, spironolactone has an androgenic effect itself, so its efficacy for feminization is typically lower than one would think based on its effect on testosterone levels. I personally found it worthless for feminization, but had all of the side effects listed above. As a result, I no longer use it.
