Sabaku no Gaara
AND I'll explain why.
Sasuke did not pierce Gaara's absolute defense with chidori alone, Kakashi had Sasuke spend almost ALL of his training time using his 2-tomoe sharingan to emulate the speed of Rock Lee. Why you ask? because as Kakashi says, the penetration power of Chidori is based on the speed at which the techique is used, Sasuke needed to use his sharingan to match the speed of the fastest shinobi he had fought, (Rock Lee) and with that speed, as well as a HUGE space and time for a running start, he was able to punch a hole through Gaara's ultimate shield.
The difference? Kakashi at this time has no Sharingan, and his speed is not comparable to Rock Lee without his weights. For this reason I believe that kid Kakashi's form of chidori would not be able to damage Gaara in his ultimate defense. In addition, without this speed Kakashi wouldnt be able to out-maneuver Gaara's standard defense as Lee was only able to take the offensive after removing his weights and revealing his true speed.
I hope this sounds as logical to you too, i was acctually just thinking about this matchup the other day lol.
btw - Gaara mid diff.