There really shouldn't be that much difference. A lot of people say you'll hold less water because Sust has the small Propionate ester attached, but it also has the massive Decanoate ester attached that is larger than the Enanthate ester and takes up nearly half of the mass of Sust...so on that basis, that can't be the reason people hold less water with Sust.
For whatever it's worth, the most I ever bloated in my life was using Sust, but that's because I was eating too much. Eat too much, hold water...pretty simple.
As for salt, just a side note based on another comment in this thread...of course too much salt can be a bad thing, but sodium is also necessary. I think a lot of guys have a misplaced fear of sodium...it can actually help you in certain cases. Me personally, I require a lot more salt than the average guy, for about 5 or 6 years I've had a sodium deficiency problem. I actually have to drink salt water sometimes to take care of the problem or take sodium caps. It doesn't cause me to bloat or hod water at all....it actually keeps me functioning quite well. Anyway, when I get bad muscle cramps, a quick slurp of salt water takes care of it every time.