I would say it depend solely on the person and the need; for example if you what to knock out a person for interagation later, or some other non-lethal reason*then Rasengan or it's evolutions*is your jutsu but if you need to put someone down for good the Chidori or one of it's varies forms are your best bet.
ITACHISPRODIGY wrote:
i think chidori is better because it pierces through things unlike rasengan
Actually if you watched the episode where Jiraiya shows Naruto what the Rasengan can do, you'd know that the Rasengan can pierce things also and do lots of damage like the Chidori. I can't choose over either, they're both awesome and powerful.