Found this table somewhere which shows the differences between the band and bypass.
Gastric BandGastric BypassLaparoscopic operationYesYesTechnical difficultyRelatively straightforwardRequires advanced laparoscopic skillsHospital stay24 hrs48 hrsComplicationsUncommonUncommon but can be seriousReversibilityStraightforwardDifficultStart of weight lossMinimum of 6 weeksStarts immediatelyExpected weight loss30-60% of excess weight70% of excess weightFailure to lose weight0.1<1%
Note - Sorry cant get the table to copy and paste - so you'll have to work it out ;-)
The expected weight lose stats were derived from a group of 1000 different paitents so are in no way conclusive, but give an indication of what the average person should/coul expect from either op as a lose.
With pure statistics in mind, if you are say 20 stone (start weight) and with a band statistically you can expect to lose 50% of your excess body weight, - in my mind that still leaves you at 15 stone, which depending on your start BMI will still leave you class 1 obese.
With a bypass and using the same start weight and supposing you lost the average 70% you'd be be 13 stone - so a bit closer to a recognised healthier weight.
Ok so this is pure fact and based on stats alone, as Serenity said a lot depends on your will power and the way you work with your tool, and as Serenity also said she knows someone thats lost a load with a band, so it can be done !
Theres 101 reasons to go for either op based on your own unique criteria and whats right for one isn't always right for the other, end of the day you will need to live and work with your chosen tool, personally i see both as a life long change, whether you have a bypass thats not easilly reversed or a band that is, in my mind this is a one way trip and personally i want my tool with me now for life.
Good luck SS