Short answer: Use Rockbiter on faster weapons and Windfury on weapons that have a 3.0 swing delay or slower.
Long answer: due to a current thread started by Vehementi here
http://forums.worldofwarcraft.com/threa ... an&t=42555 , this question cannot be answered with any sort of definitive answer. As it looks, there is a catch ingame to prevent a weapon proc from processing twice in three seconds. Several shamans have reported this negatively impacts the overall percentage of windfury procs.
In the early game, Rockbiter and Flametongue both have their uses.
Rockbiter is a good to use when:
fighting low armour mobs. AC is taken into account when rockbiter damage is calculated
as a main or secondary tank
fire/cold resist mobs
as the base default buff when soloing in the early game.
Flame Tongue is good to use when:
fighting high armour mobs, as the fire damage is constant despite AC
as a primary or secondary healer before windfury
against fire-vulnerable mobs
Frostband is good to use when:
fighting mobs that run. Yeah, it won't proc *all* the time, but it should save a chase or a shock spell to make it worth the while
frost-vulnerable mobs