I find it rather annoying to change weaponsets all the time during leveling, so I went with axe/warhorn and greatsword. Warhorn for the speed (and later signet of rage) and axe mainhand is good damage. I used sword for a while instead of axe and due to the anytimer hitting more than one mob it also synergized quite well with greatsword.
I tried to live without warhorn, but basically one of the fastest way to level is to explore a zone (or two, alternating), do all the hearts, POIs, etc. and events, so speed helps enormously with that.