Purely in terms of ick factor, most people would generally agree that shit is much more intrusive in making its presence known.
Evolutionists might argue that the reason we find the smell foul is for health and preservation reasons. Urine doesn't have such a sharp smell (unless of course you don't drink enough water or have a really odd diet... in which case your shit is likely to be really weird too).
I do have friends who faint even at the mention of blood... not sure what causes that.