I've always preferred stick over pad for fighting games. They're just more comfortable for me. I even played Injustice with an arcade stick, even though that game was arguably designed for pad from the start.
First off, for me, pressing multiple buttons on an arcade stick is infinitely easier than pad. With pad, you're better off Macro-assigning multiple buttons to triggers or bumpers, unless you want to hold the pad reeaaally awkwardly (they call it... "the claw technique"
)
You can assign buttons on stick as well, but that's more for convenience, as it really isn't necessary and your grip on the stick doesn't need to change, in order to hit buttons simultaneously. There are also a number of other reasons why I won't consider pad for Tekken:
1) Diagonals and Quarter Circle motions are much easier to do consistently on stick.
2) The difference between sticks are less marked than the difference between XB1 and PS4 pads.
3) Tekken is an arcade game and it has been since its inception. Forgive me for the elitist overtone, but learning on stick gives your progression and gameplay that "arcade authenticity".
Have you
REALLY mastered Tekken if you haven't done so on stick?
You may disagree but I don't believe so.