Kool Stop make Dura and Dura 2 pads, which both fit the same Dura Ace-style holders:

Kool Stop Dura
Kool Stop Dura 2

Apparently, the Dura 2 is (per Kool Stop) "newly designed"; Harris Cyclery call it an "upgrade" from the Dura, but the real difference - same compounds - is that the Dura 2 is thicker and has no "plow tip".

Ceteris paribus, thicker = longer life = better, but is the plow tip a gimmick, or a feature worth having? For the sake of argument, this is on a bike that would very, very rarely see mud.