What kind of restoration spell would give my character higher damage? Fortify strength or Fortify blunt?

Fortify Blunt is much more effective.

A character with 50 Strength and 100 Blunt skill does 85% of base weapon damage while a character with 100 Strength and 50 Blunt skill does only 59% of base weapon damage. For further comparison a character with 50 Strength and 50 Blunt would do 48% damage and a charcter with both 100 Strength and 100 Blunt would do 106% damage.

Yes, boosting the skill (blunt) is quite a bit more effective than boosting the supporting attribute (strength). I enjoyed reading the fine point that Dragatus put on this to really refine how much 'quite a bit' is. :thumbsup:

Of course, you could also make a combo spell that brings both up to 100, then make replacement variants that have less magnitude and more duration as your restoration power grows.