I voted for the Bannor rally spell, becuase it seems to only help with a few battles and can only be done with a civic that i find weak.
Also the Khazad Mother Lode spell, becuase it adds a small amount of gold in comparison to what a Khazad player should typically have.
I havent played enough games to actually vote, but I disagree a little bit with the comments above:
I just built an empire just around that new worldspell. I agree that Rally is useless against an early rush and that it ist quite limited...but than, once you have researched Fanatism Rally just works great. I just DOUBLED my army strength and will eradicate alle enemies i one great crusade.
Spell works just fine and fits the flavour.
It could be considered, if the demagogs might be boosted a bit. I would love the idea to reduce their base strength to, say 3 or 4, and add the Pikeman-Mechanic from Age of Ice, to join units to get a boost of 1 point of strength. (perhaps to maximum of 6-8). You could even remove the ability to use metal weapons (and raise their strength again), to give them an edge even if you lack metal (kind of an rubberband idea) That way the player can choose if he wants an endless army of suicide troops or if he wants less, but stronger troops.
Motherlode fits perfect for an already strong civ. I agree, that it might not be overly useful and doesnt have that much impact as say Raging Seas, but it definitely helps to bolster the Khazads treasury...I think the power of this worldspell is ok...
I still havent found out useful situations for the worldspell of the sidar...perhaps multiplayer surprises?!