For me, MOC, if you want detail and accuracy , Set, if you want to "play".
As @Kage Goombasays though, MOCs at UCS scale can be very VERY expensive and sourcing parts can be a pain in the under carriage. So far I've gone the route of buying a couple of UCS models and modifying them so the details are more in line with what I expect.
Personally, I've had 6 Lego Star Wars sets and they now exist only in my parts bin or serve to mod my UCS ships. I won't buy another Star Wars set again but that's only because I want more detail and want my models to have more than a passing resemblance to what I see on the big screen!