I thought it was obvious that Sasuke is the greatest raiton user in terms of mastery. And meanwhile a bunch of clueless morons argue amongst themselves about things non-sequitur and that has nothing to do with the thread.
This isn't about two raiton users battling with their respective raitons. That automatically rules out everyone on the list despite their lightning release prowess (i.e. Kakashi is stronger than Darui, but that doesn't necessarily mean he's the superior raiton user. This thread is more or less about who has the most proficiency of the art).
This isn't about any other jutsu or style. This isn't Rasenshuriken vs. Kirin. This is simply about who is the most adept user of the lightning style and art.
I go with Sasuke. Then the 3rd Raikage. Why? Simply because Kirin is the highest level raiton in the series as it's raw lightning. Sasuke is the only person in the manga shown with the ability to tame sheer lightning. No one else but him can do this. While the 3rd's signature raiton technique is something extremely similar to the Chidori in terms of mechanics and style.
Based on feats, here is a canon list of the best lightning release users from greatest to least (descending order):
1. Sasuke
2. 3rd Raikage
3. 4th Raikage/A
4. Darui
5. Kakashi
6. 2nd Raikage - We've seen nearly nothing from this guy
7. Ameyuri Ringo - Ruled out due to non-canonical likeness. Anime does not qualify. Otherwise Raiga of the Seven Swordsman of the Mist and others would be on this list.
These are the most honed lightning release (raiton) users that were listed. Again, from greatest to least.