I've use the organic and sintered for a couple of years on different bikes, either are good value vs the alternatives.
The organic give the best feel in dry conditions, and are cheap if you buy 4 pairs. In manky conditions they can be destroyed quickly (<1 ride). They last for ages used in dry-ish conditions.
The sintered last for ages in normal UK conditions, but aren't quite as powerful and make a little more noise. Alegedly cause the brakes to overheat more quickly, but it's never really been an issue for me on the bike they're on.
I've got four pairs of the Kevlar to try out, but not used them yet.