Like anything, painting is a skill you will learn with practice. I
would suggest learning to use a roller and brush. Do some research on
proper technique to avoid many of the basic pitfalls. Roller and brush
marks are definitely avoidable with proper technique and tools. Buy
yourself quality paint, rollers and brushes and you won't be sorry.
You mentioned in your post that you have seen professional paint jobs
with brush and roller marks. I would say that either the painter was
not experienced enough because an experienced painter does not leave
marks or the marks were already on the wall and the painter did not
prep properly to get rid of them before the new paint went on. Either
way, a professional would not do that. Don't judge the high quality
work that a good roller, brush and technique can do because you have
seen what you though was professional results.

I learned how to paint many moons ago from a real professional and I
remember my first day. I didn't know a brush from a roller. My boss
had me spending my first several months painting insides of closets. I
would suggest the same for you.

After you do some reading and learn the basics, start with the insides
of closets and other non visible areas. You'll need this to learn
how much paint to put on the rollers and brushers, how to properly roll
paint on the wall and how and when to use the brush.

Don' be afraid of painting, there's not much to it.

One last bit of advice. 90% of a good paint job is prep. The
remaining 10% is actually getting the paint on the wall. Every little
imperfection on the wall is transmitted thru paint and can make or
break a paint job. As you do some reading you will learn how and what
prepping is all about. Too many people skip preping and go right to
painting and then wonder why the paint doesn't look good when their
done. They blame everything from the paint to the roller but not their
technique.

Have fun and lots of luck.