It might not be my place to give advice since I'm a noob, but I would imagine most of the SC cast plays easier with a stick. Just pick whoever you have the most fun with and put the time in!
Actually, I find the opposite. Setsuka and Ivy are way easier to play on pad and Hilde is ONLY played on pad rather than stick. Granted, some characters benefit if you learn a stick - yoshimitsu springing immediately to mind, but you can play any character well on pad and some characters are arguably limited if you play them on stick.
For example:
On pad, I:
Main: Siegfried
Second: Kilik
Tertiary: Ivy
But on Stick, I:
Main: Setsuka
Second: Yoshimitsu
Tertiary: Voldo
Not because they are easier on a stick, but because I physically can't play my pad mains on it and believe me, I've tried hard to achieve that. =/