Walsall will only do a band if your bmi is below 50 (I think), i was told I could have either but my pct won't fund any more ops if it goes wrong or I didn't have the weight loss that i need. I was leaning towards a bypass because of the type of eater I am. I like cake, sweets, biscuits, chocolate, and can eat masses of the wrong foods, so I knew a band would be no good for me as i would be able to cheat but with a bypass most people get 'dumping' if they eat high sugar/high fat foods and my portion sizes will be cut as i wont physiacally be able to eat that amount as it will cause me great discomfort.
So you need to think about what type of eater you are too.