To improve general render quality, you should adjust the Shading Rate to about 0.2. I think the default is 1.0, and that is fine for most renders, but reducing that will help with quality.
If you are using Uber lights, that may be your problem. It requires higher settings, and therefore usually longer render times.
A fuller explanation of what you are seeing (with an image if possible), and also what lighting you are using in the scene would help. Also, an image of your Advanced Render settings too.
I have dialed the slider all the way up to 4
Setting the quality to ‘4’ simply means that you are using the 3Delight render engine, the other settings only use OpenGL which is basically much the same as the viewport render. You could try resetting the render options to the default, and then turning down the Shading Rate as explained earlier.