sigma 50 f/1.4
the canon samples show that the bokeh is absolute butter. almost too much butter, in fact.
i wouldn't use a macro. the lenses are designed for close focus with sharpness across the frame. they also don't have the large apertures necessary to throw the background out of focus (though i guess f/2.8 at 105 on a zoom is the same as f/2.8 at 105 on a macro, though, as the zoom might be designed with portraits in mind, the design may try to accomplish more than with the macro, which isn't)
if you don't mind focusing yourself, the 85 f/1.8 or a 50 f/1.4 would be good choices.
if you want zoom the sigma 50-150 II HSM replicates the classic portrait lengths for crop bodies.
the nikon 70-200 is about 77 cubic inches. the sigma is about half of that at 39 cubic inches. the tokina 50-135 is only 25 cubic inches, but doesn't have a motor, unfortunately.