1/2 inch impact

I use one of the MAC line of Impacts, but they are made by Aircat(Mac also has IR guns too). You can pick them up for ~150 in the Aircat branding(Maybe half what MAC charges). There is a large 1/2 and a 3/8 size small bodied 1/2 which is excellent and I recommend. I have both but the small bodied one is great for almost everything.

Note: My small Aircat did fail after tons of use but has been rebuilt, and it is not the newest model so it could have been improved since then.

Matco has an excellent line of lightweight impacts but they are pricey. Really the only guns that I have seen that are superior to the Aircats in performance and weight.