Majority of tournaments use PS3 platform. That should tell you something.
Just because the PS3 controller is better suited for fighting games (because of the non-functional Xbox d-pad)... and in tournaments, they usually use the regular controller.
But it doesn't matter if you have a fightstick.
And don't get me wrong. I love the PS3, I love the Wii and I love the 360, but let's be realistic: when it comes to multiplatform games, 360 is the favorite choice for most gamers.
I only use the PS3 and Wii for exclusive games, just like lst gen my PS2 was for exclusive games (it has a lot) and my Gamecube was for exclusive games and multi-platform (multiplatform games runs better on the Gamecube than on the PS2... see Resident Evil 4, Viewtiful Joe, Soul Calibur, etc...).