a true DS is different from an MGB and a SIPS. I don't really know much about SIPS, but I know some surgeons do those now instead of a true DS. They're somewhat similar but not the same as I understand. An MGB is a variation of the RNY.
a true DS is the most powerful of the current weight loss surgeries . It's a sleeved stomach (VSG) with a partial intestinal bypass. It tends to produce the greatest amount of weight loss and an easier maintenance (because of the malabsorption). But vitamin deficient risk is also the greatest with it, so you have to be really religious about taking your supplements.
since a DS involved a sleeved stomach, yes, there would be a greater risk of reflux with that than with an RNY. An RNY often improves - if not cures - reflux, whereas there's a risk of reflux with a sleeved stomach (note I said risk - not everyone who has a sleeved stomach develops reflux).
btw - there's also a malabsorption component with the RNY, but it's not as great as with the DS. Not as much of the intestine is bypassed with the RNY.