Some paint levels better than others. My experience has been that paint that levels well one time, may not work the same every time.
A high quality brush will lay the paint on smoother and give less opportunity for brush marks. I like Purdy's brushes. They have a good smooth feel when painting. Keep it wet. Wiping a brush off on the side of the can constantly will cause the brush to get kind of stiff and lay tracks.
The way you paint also makes a difference. Long flowing strokes will eliminate many problems and will speed things up. When you start in a corner, brush it out however far it will go, then lap your brush marks back over the last part you covered.
With a sprayer, keep moving. A little fow-trol helps sometimes. It helps level out the finish. Keep the gun close enough to the work to avoid dry spray. Keep it far enough away to avoid runs. Keep it moving.
There are lots of things that help other people and much that helps me, that I haven't listed. Sanding between coats and laying it on thick will take a long time. To get a perfect job, it will take a while no matter how you do it.