There are two broad areas of concern in treating MtF Testosterone levels that are not incompatible with each other, and the decisions are usually based on the endocrinologists previous experience.
Most 'males' produce testosterone and blocking testosterone involves several steps. One is to block the production of T and another is to block T receptors.
Some endocrinologists like to block production first but other prefer to stimulate the bodies system of removing testosterone and then block the production. In the former people are usually put on oestrogen with no anti-AAs. This stimulates an increase in Sex Hormone Binding Globulins (SHBG) which remove circulating T. Once circulating T has been removed then anti-AA can be given to reduce the production of T. The use of anti-AAs can be double edged. Androcur which is popular in Europe and Australia is arguably the most efficient anti-AA has significant side effects, the major one being the the induction of or deepening of depression. Spironolactone has significant effects on cardiac function, and in fact that is what it is most used for clinically. It is also a diuretic, which is what it was originally sold as. So in both cases keeping people on the lowest levels of anti-AA is a desire for most endocrinologists.
So depending on the base levels of T the endocrinologist may decide to promote SHBG and see what happens and then go for anti-AA. Or reduce the circulating levels of T with anti-AA and then go for oestrogen.
The decision is, or should be made on a case by case situation.
Also, of course, this is where the relationship between the endocrinologist and the therapist becomes important. If the therapist, in my case in Australia a psychiatrist who specialises in gender problems, decides that there patient has a gender identity complex and requires full treatment, then the endocrinologist goes for full treatment. If the therapist is unsure then the endocrinologist will be slower to go to full hormonal treatment.
As we know hormone changes can have profound and irreversible effects on people. The patient can very quickly have a dangerous response that can be life threatening. Hence we need the care of qualified people to look after us.
As a Doctor I trust my professional colleagues to look after me. There is no way I would self medicate.