Male Baldness Info

Does Rogaine foam or extra strength work best? Also I know that it causes you to lose healthy hair then regrow new stronger hair, but once you stop using it do you still lose the healthy hair that was there before? Im worried because im begining to go bald at the side of my hairline..and im stilll young 21…so i have a good head of hair but it is dissapearing on the sides…so i dont want to lose even more hair if i stop using it if it doesnt work… meaning if it causes some hair to be lost due to the initial stage… im really distressed over this and would really like anyones help, i thought i could escape male pattern baldness but i was wrong… please help

i am a 20 year old man who is experiencing male pattern baldness in the front. My doctor told me to use rogaine in order to help restore my hair.. but which one should i get the foam one or the liquid? and why?
thank you for your time.