Also in Part I when Naruto and Sasuke fought on the roof of the hospital when Sasuke was throwing is little hissy fit, he saw how much more damage Rasengan did to the water tank, and got even more angry.
The Rasengan and Chidori use two different varieties of force. Spiralling concussive force is transmitted into something where it begins to drill through to the back and out, leaving a gaping hole where the Rasengan's energy punched through (the water tank proves this). Although from what's been seen of all the hands-on showings against people, the damage is inflicted at the area of impact, drilling into the person rather than preserving the energy for an internal to external pathway.
Chidori was intended to be an assassination technique. I think the principal is to kill as quickly and effectively as possible with giving as little time for the victim to retaliate or cry out as possible. You greatly strengthen the penetrative force of your limbs through nature manipulation and that enables you to reach a person's vital organs with Chidori. Besides acting as a human sized sword, there's probably some scorching and paralysis damage from the Raiton itself. It may not have been intended to have the same area of impact as the Rasengan though.
They're both equally damaging in their own ways and they both require advanced chakra manipulation to be able to make. The Rasengan has the advantage of not having to form any handseals though and it seems like you need to have certain tools to be able to use Chidori effectively.
Edited by Atheck, 15 April 2014 - 06:08 PM.