I know I will be thrashed..but, I work on things on the weekend and after work some weeknights. I am not a professional working with air tools all day, every day for a living. If so, buy the highest quality tools. I bought the HF 3/8 and 1/2 impacts for around $150.
The 3/8" is rated at 200 lbs-ft and the 1/2" is rated at 625. I have had them for about 1-1/2 years. No problems. I mainly use the little gun as it is light and will fit into tight spots. Get a 20% coupon and save a little more.
Just an option to get two guns and have a large one for really stuck nuts. Good luck on your search, you'll like whatever you get.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=2623
Tool weight: 6.6 lbs.
Maximum torque: 625 ft. lbs; Torque range: 40 to 400 ft. lbs; Free speed: 6600 RPM forward, 6800 RPM reverse ; Standard bolt capacity: 5/8"; Air consumption: 4.7 SCFM; Air inlet: 1/4"-18 NPT; Overall length: 7-3/4";
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92453
Tool weight: 3 lbs.
Torque range: 20 to 180 ft. lbs, Maximum torque: 200 ft. lbs; Free speed: 11,000 RPM, Standard bolt capacity: 7/16'', Air consumption: 4 CFM @ 90 psi, Air inlet: 1/4"-14 NPT, Overall length: 6'' L;