Sorry to hear about your problem. Gleason score represents the grade of the tumor
and not the stage (amount it has spread), therefore has no role in deciding the management.
If your tumor is operable and your age is less than 70-73, you should go for surgery. If you age is more than 75, then go for brachy as surgery after that age will be associated with complications.
Both the treatments have their pro's and con's but both are effective. You should ask both of them to tell you more about the procedures and then make up your mind.
Hope you get well soon.