I like the worm-type dampeners (like from Gamma or Head). For a lot of people it mutes the feel of the racquet too much, but I have really gotten accustomed to that feel and they work very well for me.
if you're talking about dampeners that completely dampen the ping sound, anything that's long or big will do. personally, i like the wilson shock trap, it's longer than the nTrap, but looks less bulkier as well.
The Gamma Shockbuster I. I've tried quite a few (including the rubberband), and nothing else compares. Even when it comes unhooked, and it will on occasion, I can hear the difference. I may not be able to feel the diffference, but I can hear it. It will never, however, come off.
The effect of rubber bands is meant to be something in between having a dampener and not having one at all. Some think that a dampener does its job a little too well, resulting in a too-muted feel to the racquet. Using a rubber band gives back some of that feel without sounding too pingy at the same time.