Both application methods have positives and negatives. Personally, I believe in combing the two.
Take a look at these questions for more info;
<a href="//questions.house-painting-info.com/spraying-house-then-using-roller.html">Spraying house then using roller.</a>
<a href="//questions.house-painting-info.com/full-vs-spot-priming-spray-brush-and-roll-or-just-brush-and-roll.html">Full vs spot priming; spray brush and roll or just brush and roll?</a>
<a href="//questions.house-painting-info.com/spray-vs-rollerbrushing-for-exterior-painting.html">Spray VS Roller/Brushing for Exterior Painting</a>