learning render settings you need to spend time on it. production settings preset always render in good quality but it also depends on the mesh, shadows, shaders, and textures. default settings of production gives good result making shadows edges softer but then if you want some bounce in the lighting you can further work with FG and GI. So overall if you want a good quality rendering following are the main points that you should always take care of;

1.) Max Sample Level (raytrace/scanline quality drop down menu)
2.) multi pixel filtering
3.) raytracing(values of reflections refractions and shadows)
4.) final gathering (in indirect lighting tab)
5.) point density and point interpolation ( in final gathering settings)

keep max sample level to 3.
in multi pixel filtering use Gauss , value = 2.5 by 2.5
in raytracing keep values for reflections = 10 , refr4actions = 10 shadows = 20 (skip refractions if there are no refractions in your scene)
in final gathering , point density = 10 and point interpolation should be 50-100.

and i would like to know how you are rending AO?