You will need to use a roller for the broad areas and a brush for the corners and cutting in.
You could use a brush on the walls but quality and time is obviously the problem.
Obviously people are having issues with what type of gear to buy to get a nice finish.
I want to tell everyone who will listen or have any kind of painting to do in the future to go and buy a couple of paint brushes called UNI-PRO Smooth Coat...