It is difficult to get a uniform surface with brushes alone, but it is possible and is a very useful skill to have, if you hate masking with a passion like I do.
Pollyscale, Tamiya enamels and Gunze Sangyo's Aqueous hobby colors all hand brushes well, i.e. they self-level when brushed on. It's best to thin them some (Enamels with mineral spirits, and the other with a mixture of alcohol and pure water.) Tamiya acrylics don't hand brush well at all. For Gunze Mr. Color line, I use their color leveling thinner and get a very nice finish.
To get even coverage, use thin paint and a flat brush and stroke in one direction. After the paint dries, make another pass in the direction perpendicular to your previous pass. This criss-crossing eliminates streaks and gets you a level surface. Another way is to rely on the paint leveling itself so that the streaks will be gone. When I hand brush with Mr. Color, I thin it in progression until I get the thickest paint that will level itself, which is usually pretty opaque. Then I brush this on and the surface will be very even with just one pass.