Separ, I am trying to make the same decision myself and have been researching the heck of this subject. It doesn't help that the medical community is split on this subject--just like many of us. There are some facts about both procedures that are not in dispute.
First, if you have Type 2 Diabetes, there are multiple studies that show that bypass has substantially greater likelihood of resolving diabetes when compared to other surgical options. Researchers don't know exactly what mechanism is triggered by bypass that makes so much more effective--but the result is clear (particularly for people with mild to moderate T2DM who have had the disease for 8 years or less). Gastric Sleeve is also beneficial for those with T2DM, but not to the same degree.
Second, if you have acid reflux (all the time, not just after a crazy night of Mexican or Indian food), sleeve is probably not the way to go. It can make reflux worse and it can cause reflux in people that didn't have it before the surgery. The reflux can be control with proton pump inhibitors (pepcid ac etc.), but it's not great to be on those long term. In the alternative, bypass is used as a treatment to reduce reflux for people that suffer from it.
Third, gastric sleeve is a less invasive procedure (although it is still major surgery), but the complication rate between the two procedures are pretty comparable. There are some small statistical differences that favor the sleeve, but those numbers don't really have much real world significance. Some of the historical data for bypass is skewed because the surgery was done as an open procedure in many cases before 2011. It's almost exclusively done laparoscopically today--which reduced the complication rate so it's pretty much the same as the sleeve.
Fourth, the prep and recovery from both procedures is the same, so that shouldn't be a factor in your decision.
Fifth, many people that have bypass experience dumping syndrome, which makes it difficult to process simple carbohydrates and greasy/fatty fried foods. If you have a carb addiction, this will stop you from eating those carbs--and it will punish you. There's a funny story about Al Roker (who had gastric bypass) having explosive diarrhea while he was visiting the White House years ago (worth a google). You can have some food intolerance after sleeve, but it's not the same by any means.
Sixth, gastric bypass has a malabsorption component, which requires more supplementation than is required for the sleeve. There are some long term studies which show that after several years, your body adjusts and the malabsorption component is less of an issue (and less of a benefit). The jury is still out on this.
Seventh, there is a dearth of long term studies on sleeve, so we don't know how effective it will be 10 years post op and what long term issues might arise. Bypass has been around for a lot longer, so we do know that it is generally very effective for the long term. We do know that sleeve and bypass have reasonably comparable weight loss results at the 3 and 5 year mark, although people tend to lose about 5-10% more with the bypass and they lose it faster (which may or may not be a good thing).
Eight, gastric sleeve can be revised and converted to a bypass or a duodenal switch if you fail to lose sufficient weight or have difficulty controlling diabetes or reflux. The benefits of revision are limited when compared to your first surgery (at least as far as weight loss is concerned). The options for revising gastric bypass are more limited. That said, many bariatric surgeons believe that you should go with what they consider the more effective and proven surgery out of the box and that shouldn't go into your primary surgery thinking that if doesn't work out you can just switch it up later on. Moreover, there is a higher complication rate with revisions, revisions are less effective than primary procedures and some insurance carriers have more challenging criteria for qualifying for revisions than primary surgeries.
Ninth, for people that: (i) extremely high BMI's (over 70); (ii) are older (over 65); (iii) have pulmonary or heart issues; and (iv) have had significant abdominal surgery in the past, gastric sleeve may be preferable. It takes less time to perform; therefore, you are under anesthesia for shorter period of time. It also doesn't require any rearrangement of the intestines/digestive track.
Tenth, if you need to take time released medicine or NSAID's for pain management, gastric bypass may not be the way to go. You can develop ulcers in the unused portion of your stomach and they are not easy to treat. This is definitely a disadvantage of the bypass IMO.
I am sure there are some other factors to consider, but these are some of the big ones that strike me as important. I have to make the same decision as you. I am a 44 year old man, 5'9'' and I weighed ~260 at my highest weight (around 245 now). I have mild-moderate T2DM, but a relatively low BMI (just over 35). I am leaning towards bypass because I really want this procedure to resolve my T2DM and I want what I hope will be the most effective. I will have to change some of my medications in the future if I go this route. The surgeon that I am currently working with is a big advocate for the sleeve. I have an appointment to meet with another surgeon in a couple of weeks for a second opinion--so I have definitely not made up my mind yet (and I was also told that I can change my mind last minute--although I assume that means a few days before the surgery date). Anyway, good luck with your choice and ask as many questions as you want!
