On a local asset by asset basis, there's really no arguing that TO:1886 is more impressive than UC4 (i'd argue it's by far the most graphically impressive 8th gen title we've seen). That's not particularly surprising though. 1886 has a strong focus on its local surroundings, while UC4 is spreading its resources/LOD ranges over surprisingly large areas, and also filling those environment with a huge amount and variety of animated/physics based flora and foliage.
That said, i'll wait until we know UC4's final performance rate before deciding which i believe is overall the biggest accomplishment. If ND have decided to settle on 1080p/30fps permanently, then i'd expect to see some pretty significant graphical improvements by launch. If they're still targeting 60fps (likely a variable), then holy shit, what they're showing now is mind blowing.
Seeing as they already have a fairly stable 1080p/30fps build so far from launch, i'd say the variable 60fps target is the more likely possibility right now, but we'll see.
I'd like to add that i adore 1886's art style. Regardless to which route UC4 takes, i'll likely still think 1886 is the "better looking" game. They've done a stunning job of capturing both the sooty/dirty feel of London at the time, as well as the glamour the elite of that period enjoyed.