CP or Ingersoll seem to be the old standbys. I've used a CP 734 for years. It isn't the most powerful 1/2" made but it's lighter weight and I like the push button direction change. HP makes a bigger 1/2" than the 734 if you want more torque. Ingersol makes a darned good one too. I forget the model number, but the one I used on the harvest was about the same physical size as the CP 734 but had more power and speed. It also was heavier. The direction change button, or dial depending on model of IR, is a little unhandy but maybe it's because I'm not accustomed to it.
Both brands have quite a wide selection to choose from so you do have some choices. When I was looking for a 3/8" air wrench I requested the fastest RPM air wrench CP made for zipping the nuts off of bolts with a slotted screw driver head. The one I ended up with is wicked fast. The nut unscrews crom the bolt so fast it propels the air wrench up away from the bolt and the nut goes spinning across teh floor. Just an example of the choices you have. Jim