I run MorphOS 3.7 and OS4.x is visually more appealing out of the box.
It's really a matter of taste. I don't like the look of OS4 too much. In my book it looks rather non professional and a bit old. That said I don't like the default MorphOS skin (Ferox), too. But the clara skin is pretty neat IMHO: clean, modern and Amigaish.
Well, taste differs...