I ride with a standard tee shirt, nice and loose and drafty. Never cared about being aerodynamic (or looking that way), and never worried about a tan line, since the sleeves flap around enough to blur it.
My one problem with the sun was the tops of my thighs, which got pinked pretty good on the first long rides of the year. SPF 30 was good enough to prevent it . . . when I remembered to put it on. (Which is to say, the second long ride of the year.)
