Funny this should be asked, because I just bought a used Roland S-760, fully-blown with monitor, library, and drives. I have wanted to do this for some time, and the right unit with the expansions I desired presented itself at a nice price.
Why, in this day and age? Simply-put, the gorgeous sound. It uses the same multimode filter as the Roland JD-990, and the character of the Roland S-760 is absolutely perfect for pads, strings, and atmospheres. It has that "special Roland color" I love so much. I have previous experience with the S-series engine as found in the DJ-70mkII, but now I have an interface to deal with the byzantine, if powerful, architecture.
For me, between these two choices, Roland S-760 all the way.
My other hardware sampler is a Yamaha A5000. 8)
cheers,
Ian