Ditto both comments by waross and itsmoked, plus my experience:
1) residential or commercial (spec grade) will become weak over time in the clamping force to hold the plug in. If plugged into daily or more frequently, you'll find that plugs just fall out oun their own after a couple years.
2) Hospital grade will never get weak, they seem to last forever even in really demanding service. Safety type just has springy covers that keep young whippersnappers from poking mom's car key in there.
3) Haven't experienced "industrial grade" personally, except in twist-lock configurations.
4) Brand does make a difference. Stick with the major players like Hubbell, Bryant, Arrow-Hart, Pass & Seymour, etc...
Good on y'all,
Goober Dave