I would recommend Apeks XTX-50, XTX-50 or ATX-40 second with a DST or DS4 first. Their is nothing wrong performance-wise with the XTX-100 and 200 but I would not recommend them. First, they are more expensive. Second, they don't breath much different if at all from the 50. Third, if you decide you want to go into doubles their hose routing is not very good. If for some reason your heart is set on a 100 or 200, go with the 200 as the orifice is replaceable on the first stage.
---------- Post added February 12th, 2014 at 09:27 PM ----------
None at all. It is a marketing play to differentiate regulators. It reminds me of Sears where they used to rate products good, better, best.