Never have found any synthetic herl that I liked, but I do like to use a couple types of synthetic peacock dubbing. I like the Ice brand in peacock for larger flies, it has a nice sparkle and great highlights. Arizona Synthetic Peacock Natural dubbing makes a nice substitute for smaller flies. It's cut up much finer and you can touch dub it onto the thread.
"Have no fear of perfection - you'll never reach it."