I'm with Crenwelge, Ingersol Rand is pretty hard to beat. Especially the 2135ti. The 2131 would be my next choice, you can find those pretty reasonable in their assorted variants. Matco, Mac, and Cornwell all have their own rebranded versions of it, usually with their own color scheme and an increase in price. Lowe's also has them. They put out around 800 ft/lbs in reverse, 600 in forward. Not as much as the 3135 (1100 reverse, 780 forward), but they get the job done very well. The 2131 weighs about 1 pound more than the 2135ti. Then there's the old standby, the IR 125. Those have been around forever it seems, IR still makes them, with some upgrades. They put out 450-500 ft/lbs, depending on variant. You can find them for around $100, new.
As far as electric, there's really only about 3 I would even consider for automotive use, Ingersol-Rand, Snap-On, or Milwaulkee. Of the three, the only one I can really give any feedback on is the Snap-On, since I have one. Its performance is about on par with the IR2131, I have only come across a few times I needed to break out the 2135 to get something loose that it couldn't. The only complaint I have, and this really goes with any electric, is when the battery goes dead on you, you're stuck until it charges up if you only have one battery (I have 2 btw).
Now, on 3/8 impacts, again, Ingersol Rand is the way to go. The 2115 is the best on the market, it'll take lug nuts off 1 ton truck no problem. For electric, Snap-On has a very good one, but it is pricey. Both of these guns will do things lower priced 1/2" guns will not do, though.
