Preferably, all key holders are characters designed solely for this ala Pongo or Havardr. As their only abilities include:

Larger(if wanted)
Smarter
Can Talk
Whatever ability the key has
Natural abilities of said animal(real or mythical)

Pongo and Havardr are good examples of what I'm looking for.

That said, I do have an eagle key, but if I get a second one, it'll be one of the second level keys, as mentioned in one of the earlier posts. 

Though a turkey would be interesting. Hahah.