Raptors are essentially better Dilos. Whe lacking the poisonous blinding spit of a Dilo, they have a much better DPS due to their speed. In groups of three or more they benefit from a pack boost, and in groups of at least four I notice they tend to take on bigger threats on the Ark (notably Sarcos and Kapros). Plus their pounce ability is not to be overlooked.
In short, tame Dilos for the early game, but Raptors as you move into mid game.
Thank you for coming to my TedTalk. Up so newbies can see :)