Since Futon > Raiton - I would say Chidori > Rasengan since on every clash outcome is equal
Err... If Futon > Raiton... Wouldn't Rasengan > Chidori??? That is also after complete mastery of the jutsu Naruto managed to add Futon to the jutsu...
Honestly I feel like the pros and cons of each jutsu make them perfectly balanced... Rasengan is the peak of shape manipulation while Chidori is peak of elemental manipulation... Chidori has enhances user's speed and reflexes naturally, but without a sharingan, tunnel vision would render the jutsu suicidal, also requires a solid lightning affinity... Rasengan has no elemental requirement, but has been shown to be possible to add an element to it... Without adding an element, the jutsu is still more cost effective in terms of chakra usage... Kakashi, who is arguably the highest ninjutsu master in the village, said he could only use it 3-4 times as my memory serves when he was teaching Sasuke the jutsu... I can understand Naruto has near infinate chakra but it still never appeared to be chakra intensive, just focus intensive... In terms of base power, I would say Chidori is stronger, In terms of potential, Rasengan is stronger, In terns of usability, Rasengan is stronger, In terms of speed, Chidori is stronger, In terms of full hit potential damage, Rasengan is stronger, In terms of glancing blows, Chidori is stronger... Overall I would say pretty much equal overall, outside of special senarios, both are pretty much one hit kill jutsu...