I'm guessing this has been posted before but my search was not very lucrative.
Giants should really reward more (or less) favor for donations that go along with their corresponding skills.
e.g. Zill gives more than any other giant for ores (secondary giants still give slight bonus too).
Spriggan gives more for Loam/Jellisac
Alth for tinkered objects
...and so on. Right now, the giants do not have distinct enough personalities.
Obviously, just my opinion, but it doesn't seem too difficult to implement (other than balance, and what do you do with Cosma, etc.).
Cheers.