Are you considering electric or pneumatic? IMO the air impact guns are way better than any electric, so if you have an air compressor i would definitely go this route.
If bulk is an issue though, the dewalt 18v cordless might be the tool for the job but is is not 1/2in (you can get adapters) and not as strong as a corded or air impact driver. You will find a billion uses for this tool as it drives in screws and bolts so easily and it is relatively light weight.
If you want to go air. I have had great luck with my Ingersoll Rand 1/2-inch Air Impact Wrench.
If you want to go electric corded dewalt and makita both make great tools.
