I love using the simple brush to apply paint. The bristles create a handmade texture on the paint surface and you use much less paint. Cleaning-up is also simpler. But, brushing on to the expanse of a broad wall is probably not the quickest way of applying your paint. You're going to need a roller.
These days, good quality water-based acrylics are manufactured with low amounts of VOCs. Basically, this means that there are fewer chemicals in the paint that off-gas. The down-side to this health benefit is that your paint dries more quickly, so you'll have to adjust your painting technique to achieve a consistent finish to avoid "picture framing".
So, all you need to do is cut-in progressively. Brush along the edges first making sure that this area is only slightly wider than your shoulders. Then, while this cutting-in paint is still wet, load your roller and apply the paint from the centre, rolling up, then down. Cut-in, roll, back-roll in the same direction and work your way across the wall with this consistent technique. The final result will be an even, smooth and flat finish that looks professionally applied. Easy!
I hope that helps and please send me an email if you have any questions.
Long, consistent strokes in the same direction will give you a great finish. And remember, whatever the paint or colour, you'll always need a minimum of two coats.