With aluminum, I doubt there is any benifit of one over the other. Surfaces that have a texture to them require the action of a brush or roller to work the material into the texture in order to get the protection of a film.
I'm not much of a fan of spraying just because it can be messy. If you decide to spray, use an airless unit. Air powered machines (including HVLP) don't push the paint fast enough, you'll be all summer trying to finish. Piston units like the Wagner Power Painter are, in my humble opinion, troublesome at best. I've owned a few of these kind of sprayers, and they all worked better as boat anchors.
On a completly differnt note, when I paint aluminum siding I prime it with Brunning's "Grabber Plus". It has the best adhesion to slick surfaces of all the primers I've used and its easy to use.