In regards to out of he box, Id have to say MorphOS is the best looking Amiga-oid system.
OS3.9 is nice and clean, but requires a bit of tweaking of things like Reaction, MUI, fonts, etc. before Im happy (disregarding birdie and visual prefs, or afa_os for the moment). OS4 doesnt stray too far , mostly doing the theme creators take on those tweaks.
Overall though pretty much any OS can look similar to any other these days, so its all down to the artist of the themes rather than one system looking better than another.
