they're completely different jutsus, if your talking about sheer power, then rasnegan is better as jiraya said "i'll teach you a jutsu that is better than chidori"
but this thread is mostly opinionated and most people just go with whichever looks cooler which would be the chidori(i think raikari makes more sense but whatever)
chidori requires immense speed, and a good eye to see the counter incase the chidori fails to kill somebody. so far we've seen the chidori and rasnegan clash only straight on. but, if somebody has mastered chidori they can use it to surprise the enemy like kakashi did in the manga (when he was young) and just went from target to target, rasnegan cant do that.
rasnegan requires you to be able to control and harvest your chakra into a sphere and never let go of the concentration you put in it otherwise, it will fuck up. when the rasnegan hits most enemies it causes the enemy to spin or something, this shows you the kind of rotation control needed to keep the rasnegan in a sphere form. powerwise, i'd say rasnegan is stronger IF you were just counting on power but we see the chidori puncture a person a couple of times but we never saw the rasnegan do this, partly becuase chidori looks in the shape of a chakra made blade that can cut through anything, while rasnegan just smacks into something and bulldozes it. the speed used to make the chidori strong is what gives it the power to penetrate a person's skin, while naruto's rasnegan is just him running at a enemy and sticking his hand out.
i vote for chidori because its cooler but i really dont think you can judge them.