Spironolactone vs Finasteride for male pattern hair loss - which one is best?

Spironolactone is a blood pressure medication.  It is not a medication that is prescribed for male pattern balding.  It is best to consult with your doctor for an examination and treatment options.

I have not heard of Spironolactone being used for hair loss in men and am not aware of any studies.There are other adjuncts which might be beneficial in your case such as Minoxidil,Low Level Laser Light therapy and/or PRP(Platelet Rich Plasma).

I do not know of anyone using spironolactone in male pattern hair loss. You should have a consultation with a hair restoration surgeon to have your hair and scalp evaluated, and all the options available to you besides finasteride discussed, including the addition of minoxidil 5%

There is a simple answer - finasteride is licenced for male pattern hair loss and spironolactone is not. This is based on research evidence not anecdotal opinion. 

Spironolactone causes enlargement of breast tissue in men - a phenomenon called gynecomastia.  Spironolactone causes gyecomastia in well over 50% of men using doses 150-200 mg daily. it decreases testosterone, and increases free estrogen levels. This can occur with finasteride but is less common. Overall, about 1:300 of men (0.3 %) using finasteride will develop gynecomastia. Spironolactone is not commonly used for hair loss in men. 

For regular male genetic hair loss finasteride is an effective drug but when it does not work well, it may reflect that the hair is advanced to such a degree that it will not respond to any combination of drug. Adding spironolactones is a very unusual addition and something I have no personal experience with.