Rockbiter vs. Flametongue

This is to all our shamans, help a mate out. I'm trying the shaman way of life, but am a bit unsure whether I should use Rockbiter or Flametongue as my basic weapon buff.

So for the calculations, then. Flametongue is based on weapon speed, right? And the lowest weapon speed in the game is 1.0 sec, right? So if at my level Flametongue (Rank 1) says 4.5-13.8 dmg per hit, wouldn't that then mean that it basically increases your dps by 4.5?

Rockbiter (Rank 2) gives an additional 4 dps, so in that sense Flametongue seems to be better. But is there something I'm missing here?

Also, Flametongue is fire damage, so it ignores armor but can be resisted. Rockbiter, on the other hand, is just added dps to your weapon damage, which in turn is mitigated by armor. So with all this said, would it be better to use Flametongue instead of Rockbiter? Of course, until I get my hands on Windfury.

It would surely depend on the type of enemy that you are confronting ....and wind fury has its limits aswell.