I bought one of the Ultimate Gun Slings last month and took it on my mule deer hunt. It was very comfortable and pretty much non-slip. It gives much better than the leather slings to act like a shock absorber while hiking but you can still get wrapped up pretty solid for shooting. The website has some videos on it.
I use these www.quakeinc.com/The-Claw-Rifle-Sling.php on my Muzzleloaders...The best that I've found to keep the rifle from slipping when walking...These front heavy guns have a tendency to flip upside down when putting the stalk on.