The type of bristle affects brush longevity more than the look of the finish. It might be hard to clean a china bristle brush used in latex paint whereas oil paint can ruin a nylon brush. That said, it is difficult to avoid leaving brush marks with a cheap brush.

Drips and brush marks are often marks of inexperienced painters. You might just need some practice. Some people, however, never get it. It might be genetic. My wife and her father painted a railing at our house. She wanted to move on to an interior room. After seeing their mess, I had to be rather firm in my opinion of their suitability for the next project.

ionized,
Thanks for the reply! Yes, I think I missed getting the painting gene. I did look up "How to paint a room" & found lots of tips which may or may not help. The door came out ok after the second coat-I lightly sanded the drips(before 2nd coat) & while not perfect I don't think anyone but me will notice. Thanks again,
Susan

I always use foam rollers on doors. Much easier than brushing and no brush marks, though there are those who like the look of a brushed-on finish for a door.