Kizaru has not shown the slightest indication of caring for the safety of the people on the archipelago, blowing things up left and right. Aokiji, on the other hand, helped a group of stranded travellers across the sea.

Aokiji was reluctant to needlessly capture a wanted criminal like Luffy because he had no direct orders. Kizaru, however, wouldn't mind rounding up all the bountyheads around him even though the only one he is obligated to capture is Luffy.


Now that I think about it, the animal in their names may be very indicative of the admiral's temperament.
Aokiji - pheasant: Calm and does not resort to violence needlessly
Kizaru - monkey: laid back and mischevious, but quick to anger and get violent
Akainu - dog: my guess is that he probably the most loyal to the cause of the marines, and is completely ruthless to all those denounced by the WG from an innocent child to a dangerous criminal (sort of like a guard dog)