You have not said for sure.
I am going to assume you are asking about Nikon lenses.
Here are reviews of both lenses:
There should be little difference in bokeh.
Both lenses have 7 blades in the aperture device and the number of blades will usually make the most differences in bokeh (more is better).
In regards to grain (noise), when using a DSLR camera, 24 MP should make little difference because of the large size of the sensor assembly.
Remember a 24 MP picture file will be quite large and you can not get as many pictures on a memory card.
The extra MPs come in handy if you are doing lots of cropping.
If you are printing 4 x 6 inch pictures, 24 MP is total overkill.
If you are making slide shows with lots of pan and zoom, 24 MP gives you a chance to make some dramatic effects. You can make the slide show look like a movie.