I've always had good luck with rubber cat whiskers--the thing that a lot of folks don't seem to think about is your silencers can be tuned for best performance, just like your brace height. I start with a "naked" string, find the sweet spot for the brace height, then tie the silencers on around the string so I can adjust them. I've seen major improvements by moving the silencers up or down the string just an inch or so on some bows.
I haven't tried them yet, but I've heard a lot of good comments about Bowhush products as well.
As far as the string material, that can vary--see the thread about a bow not "liking" FF. Some bows will be quieter with dacron, some noisier. I shoot Dynaflight '97 on my personal bows, and get comments on a regular basis about how quiet they are.
Chad