Rasengan > Chidori period...no arguement...no comparison...why???? because When you talking about Rasengan, Rasengan got 8 Grades to it.(meaning 8 lvs)

Manga Chapter 151- Jiraiya said, " to appreciate the LV of difficulty for Rasengan, The 4th Hokage was 6 grades above the second. A Ultra-high grade LV, in order just to comprehend the Jutsu, Naruto needs to be 3rd grade lv jutsu." So Naruto only at the near Minium of the truth Rasengan Power, lv 3 Rasengan was twice as hard as LV 1 and 2 combined, each LV is a whole new different LV. LV4 could be has hard as LV 1,2,3 combined and LV 5 could be LV 1,2,3,4 combined and so on....

A ULTRA-HIGH GRADE LEVEL JUTSU, please don't compare Rasengan Vs Chidori....unless your talking about LV 3 rasengan but i would call a LV3 Rasengan = Chidori.

Overall Rasengan > Chidori.... BY very very very very very FAR