Definitely based on what is best for you. When I had my consultation with my surgeon, I was pretty sure I wanted the sleeve as I thought it would be 'easier' (I was thoroughly misinformed haha), but when I spoke with my surgeon, ran through my medical history (which included a high BMI, an underactive thyroid & PCOS), he advised that the bypass would probably be more effective for me.
BUT, at the end of the day, it is your decision