I went into my initial consultation thinking that I wanted the sleeve because it seemed like a less extreme, less risky surgery, but the surgeon recommended gastric bypass because my BMI was over 60 and gastric bypass results in more weight loss on average (as NovaLuna said above, some lose more and some lose less than average, but gastric bypass gives you slightly better odds).
I did more research in the months before my surgery and by surgery day, I was confident that gastric bypass was the right surgery for me. I've never had GERD, but I've seen a lot of people who get the sleeve talk about developing it (or existing GERD worsening), and I've seen a lot of people who get revisions from sleeve to bypass, either because of GERD or because they didn't lose enough weight with the sleeve. I don't want to get another surgery, so it seemed like bypass was the way to go to minimize my chances of needing it.
I think I also had some misconceptions about the risks of gastric bypass. Nowadays, bypass and sleeve have very similar rates of complications, so neither is significantly safer than the other. The sleeve has a higher risk of GERD, and bypass has a higher risk of ulcers. Some doctors allow sleeve patients to take NSAIDs (although I believe it is still not recommended), while NSAIDs are not allowed for gastric bypass patients. You need to take supplements for both, but sleeve patients have a better chance of being able to stop taking them eventually. There is a higher chance of dumping syndrome with gastric bypass, but some people consider that a benefit because it stops them from eating things they shouldn't.
Remember that the decision is ultimately yours, and you have the right to go to another surgeon for a second opinion. It's a big decision, so do your research and make sure you can live with the decision you make. Keep in mind, though, that the surgeons are experts who have seen lots of patients and have a pretty good idea of what surgery would give you the best outcome.