i think joints give a more realistic result, just take longer to set up.
a- u have assymetrical deformation, the right side doesnt always look exactly like the left side of face, which is more realistic and "non-linear"
b- joints rotate in a perfect arc, whereas blendshapes have a linear motion, for instance a blink blendshape would probably require an in-between blend shape to properly go over an eyeball, a joint can simply be rotated perfectly over the eyeball.
c- with joints u can have a pivot to freely move around to get different motion all the time, which is realistic, since humans dont make the same exact movements twice.

d- with a joint facial rig, u are still free to add blendshapes over your rig and use joints movements to alter them all u want; and also u can create anumber of heirarchy of groups with the joints and create tons of set driven keys for tons of poses.

but that really takes time and a good team of TDs to set up.