Originally posted by: BOARD_of_command
The difference between chidori and rasengan is not their power difference, but their efficiency. Sasuke can only use 2 chodoris in one day, any more will kill him. Naruto can use rasengan over and over and over...and over without any damage to his body.
Also, rasengan doesn't require any seals so it's moch more versatile.
e.g. You got your hands tired up behind you, but you can still use rasengan to cut the rope and free yourself. You can't do that with chidori.
You can use rasengan for a lot of things without worrying about anything, but you can't do that for chidori since it takes a huge toll on your body.