Pad vs Stick comes down to pure preference. It's really tough to decide especially if you're so used to something. If you want to start playing on stick, you gotta dedicate yourself to it and get used to it.
As far as sticks go, get a PS2 one, they have good convertors for both DC and Xbox, so that's the way to go.
The next order of business on deciding is whether you will go Japanese or American. Japanese style is like the Agetec DC stick aka Green Goblin, or the Tekken 5 Hori stick that came out here. American being the Street Fighter Anniversary stick from Nubytech. (Which IMO needs to be modded with real arcade parts)
American sticks are more circular in range of motion and have a wider throw/pull on the stick. Japanese sticks are usually by default, square gated and have a more restricted range of motion but require less input to be able to perform certain moves.
Buttons are buttons, but I'll say this, Japanese buttons feel much more comfortable. Sanwa buttons(not available on any retail stick except for the Hori Real Arcade Pro SA) are so comfortable and you don't even have to press on them hard for an input to register. Hori buttons are good too, but compared to the Sanwa buttons, they're nasty. American buttons are usually concave or convex. The better being the ones without the 'dimples' as they can actually hurt your fingers easier when you're trying to 'mash' out of certain moves etc.
That's all for now, I just woke up.
Back to finishing the Tekken 5: Dark Resurrection combo vid.
Btw, Tekken Zaibatsu is going to start the ghost system really soon, and it's going to feature some really cool listing options, be sure to check it out.