Honestly, I don't know what you're talking about with "finger agility" and all that nonsense because my little sister who doesn't play video games could probably learn this move in one minute using the C-Stick.
I wasn't trying to argue what's best, only giving what I accomplish the slide with, but if you want to take that route...
This is the C-Stick = (C), this is A = (A), this is the analog = (O)
To use the C-Stick method, you either have to use another finger to press (A) or (C), or move your thumb (Which is more common, another finger would void this math but be rather tricky for a casual gamer).
ADC = Distance to reach (C) from (A) , TRM = Thumb reverse momentum from moving your thumb down and immediately changing direction and momentum to up, (B)D = button direction, (A)R = A-Button release
C-Stick example:
(O)F, (A), ADC, TRM, (C)U
Run forward, press A, move thumb to C-Stick, Reverse thumb momentum, (C)U
Total time = ADC + TRM
Analog example:
(O)F, (A), ADC / 3, TRM - TRM, (A)R, (O)U, (A)
Run forward, Press A, Move Analog, There is no momentum due to your thumb being still, Analog-UP, Press A
Total time = ADC / 3 + A(R)
You can't honestly tell me you think moving your thumb all the way down to the C-Stick is faster than simply repositioning you thumb on a lesser distance and repressing A.