I love the 135mm f/2, but it's depth-of-field is about 1 nanometer when it's wide open, plus it's pretty soft and the chromatic aberration is unforgivable. Also, I tend to blur shots with it, employing seemingly normal shutter-speeds. (Not a great combo when you're shooting action photos.)
Basically, I want Aperture Priority with a fail-safe shutter speed.
My solution? Set it to M, on a shutter speed of, say 1/500 at f/4. The DOF is narrow but forgiving, and it's sharp as hell. As the sun sets, I let the ISO figure itself out. No sweat.