Actually its vanheim and helheim then niefelheim but anyway. As ironhawk said the traditional van/hel bless is f9w9 granting outstanding attack, defence, speed, amount of attacks and damage capability to already strong, stealthy units with glamour.
For niefelheim its usually some combination of water, nature and earth (usually earth and nature). When im playing niefelheim i like this build:
Cyclops
Imprisoned
e9n6
Dom 5
order 3
prod 1
cold 3
growth 1
misfortune 2
magic 1
He has a very nice bless for them, granting my giants 18 prot, 4 reinvig(they have 4 enc), 6 or 7(cant remember which) regen while still having nice scales, good research ability, access to (very useful, especially when forging) items my nations cant forge (at turn 36 but still...
), saves slots on my jarls who suddenly dont require (but can still use) reinvig and/or regen items.
Of course, by the time he comes out you will have plenty of research so you can use the cyclops himself as a very nasty SC (29 prot, can cast summon earth power, gaias blessing, personal regen and has other very nice stats aswell)