Depends what the intended use.
For professional use, pneumatic, I like IR's titanium line, its light, quiet and strong. The 3/8s will do almost everything required in a normal shop, and I think Ive only had 1 or 2 things the 1/2 wouldnt take off.
Professional use, cordless electric, get something strong with rebuildable batteries, because batteries are high and you will wear them out from using it everyday, Ive used makita, IR, craftsman, snap on, and dewalt, pretty much liked them all.
If you are just using it for changing tires every once in a while and using it for hobbyist stuff, I would buy a cheap cordless electric impact, a few years ago there was a 220ft lb 1/2 inch drive china one that everyone rebranded and sold as their own, you could get it for like 80 bucks, and it was plenty for junkyard crawling or the occasional tire change, then if it dies a few years down then line, you can look back at how much you used it and see if investing in a good one is worth it.
I think this is the cheapy I used to see in diff colors everywhere. its on 64 dollars and it has good ratings
http://www.amazon.com/Tradespro-837212-24-volt-2-Inch-Cordless/dp/B00E6EF826/ref=sr_1_1?ie=UTF8&qid=1428025608&sr=8-1&keywords=cordless+1%2F2+impact
I think this is the set I use at the house now. Truthfully I use the 3/8s drive like 100 times more, it fits better in the hand, and most times I just break something loose and use it to pull the rest of the way off.
http://www.amazon.com/DEWALT-DCF880HM2-20-volt-Lithium-2-Inch/dp/B00BWFIKJA/ref=sr_1_3?ie=UTF8&qid=1428025608&sr=8-3&keywords=cordless+1%2F2+impact
I think this is the one I bought my brother a year or two ago for christmas he loves it but he does metal working, and mainly works on tractors and trucks so he normally has more room than me, and he said he loves it.
http://www.amazon.com/Craftsman-Impact-Battery-Charger-Included/dp/B003A9HGIM/ref=sr_1_12?ie=UTF8&qid=1428025608&sr=8-12&keywords=cordless+1%2F2+impact