All of these "is X weapon better than Y even if X is faster?" questions can be answered by looking at the weapon damage, if (Top end + Bottom End)/2 is higher on the X than Y, then it's an upgrade for sure.
For example:
http://www.wowhead.com/item=81089 463 iLvl 2.6 speed
http://www.wowhead.com/item=87012 502 iLvl 1.8 speed
Axe: 6335 avg. damage
Dagger: 6308 avg. damage
in terms of pure damage, the dagger wins, but the increased stat gain is:
+169 Agility
+145 Haste
+324 Hit
-261 Mastery
Which should make the dagger winner in this case.