according the the various makers... the bungee type is supposed to be more comfortable... can't even find any written reviews online. Only thing I found is this one video review:
http://www.youtube.com/watch?v=MIB-aWhoO48
edit: btw, the only viable advantage I see to a bungee type sling is that it would tighten up when the sling wasn't around you so there wouldn't be excess sling hanging down that could get in the way should you choose to shoot without wearing the sling.