The quality or the Bokeh can also be dependent on the focal length (of a zoom lens), the type of background behind the subject, and even the composition of the shot. The pictures below I took for the Pentax-A 35-105 f3.5 In-Depth review I did and can be seen in that review in the In-Depth Review Section. The first shows the very busy Bokeh with a brighly lit background. The second IMHO has much better bokeh, even though the lens settings are almost the same. Same focal length and almost the same aperture, completely different background and very different results. The bokeh is actually busy in both shots, but adds to the second shot and takes away from the first. The composition actually plays a part in the appearance of the bokeh here. The lesson, at least for this lens, what works in one situation does not always work in another.
Pentax-A 35-105 f3.5
@35mm f3.5
Pentax-A 35-105 f3.5
@35mm f4
I discovered later that the bokeh is actually much better at longer focal lengths, but I don't have any examples with me here at work.