You should only be tq'ng the lug nuts to ~80ftlb. That should be easy enough to remove with one of those 4-way lug nut tools. If not, use the tq wrench to break the tq.

If you still feel you need to buy an impact get a cordless (battery) one if all you're going to do is put lug nuts on/off. Those cheapo Harbor Freight ones will do just fine for installing wheels. Otherwise, get a Craftsman, Dewalt, Snap-on, etc one.