I think the dinosaur most people wish to be better is the Parasaurolophus, probably because it is so common.
After a while I finally had an idea how to make these useful: the ability to make a trumpet sound with it's nose-crest-complex which buffes allies a little bit so you would have a much weaker, only ally-related version of the Yutyrannus.
EDIT:
I came up with other ideas:
Araneo: a string-shoot-attack that can be used either as a grapplinghook or a zipline. Also it should be able to walk on ziplines and walls.
Glowtail: the ability to be placed on walls
Liopleurodon: please, Charly, make the current Liopleurodon a rare version like the Unicorn and ad honest Liopleurodons you actually can use to snap somebody's ass of!
Mammoth: the same ability the Kentro has, please
Megalodon: blood sense: the ability to find injured creatures (Also the model is one of the few that actually are HORRIBLE)
Oviraptor: collect eggs in your base
Raptor: latch on bigger creatures + pack bonus
Terror Bird: a beak-attack that can push smaller running creatures, like Megaloceros, to the ground.
Trike: the Kentro ability or the Wooly Rhino ability, please