the ideal focal length for portrait is mid tele, but portrait can be head shot only to full body length, some time will includes environment also.
So you can use various type of focal length lens, to do portrait shots, depends on how the way you compose/pose your subject.
Depends on how far you can stand. For full body portrait usually people use 35mm or 50mm on DX (more of 35mm actually)
By the way, bokeh is the quality of out of focus areas - not the quantity of background blur. That depends on the construction of the lens itself, not the focal length.
For outdoor (ie enough working space) full body shots, I like 85mm, but then again I do not have access to a fast telephoto lens as suggested by mod catchlights...