Let's get this much out of the way: Shoryuken for shoryuken, the Mad Catz Street Fighter IV FightPad is a vastly superior instrument of destruction compared to the standard Xbox 360 controller.
Verdict: In one sense, the verdict is that straightforward—the fantastic floating D-Pad and arcade-style six-button layout crush the regular Xbox 360 controller when it comes to fighting games. The FightPad makes my game so much better, so much more precise, I don't think I could go back to using the old pad.
Here's what I mean: With the old pad, on average, I would successfully execute Fei Long's rising dragon kick (or insert any dragon punch-based manoeuvre) about 5-7 times out of 10 tries. With the FightPad, it's like 9 times out of 10. Moves requiring 720-degree motions, like Zangief's super, come off much easier as well, and exactly when I want it to (when someone's up in my face—PILEDRIVER). Back, forward, back forward style specials, like with Honda or Blanka, aren't noticeably easier to perform, though.
The shape and layout of the FightPad kinda reminds me of a Sega Genesis controller, and is for the most part, excellent, though if you have elven hands it might feel a little too big. For me, with medium mitts, it fits perfectly, no matter which way I hold it (I actually turn my right hand palm side down, so I can mash the buttons with my fingers whenever I play fighting games) and there's some breathing room for gorilla-handed people too.
But there are some things you should know about that would be dealbreakers if beating people didn't matter above all else. Numero uno, on the Xbox 360, this sucker is wired, which is lame balls for a $US40 controller. It also feels very cheaply made, with glossy plastic Mad Catz found and melted down after it fell off a Christmas ornament truck. The rubber coating on the sides and back helps a little bit. Last, the sound quality coming through the headset on this thing is really terrible, like I was stranded on a desert island with a mobile phone from 1987—it's noticeably crappier than it is on the regular Xbox 360 controllers.
Those things said, if you wanna do better in Street Fighter IV—or any fighting game really, since it worked fantastically with Samurai Showdown II and SFIITHDR as well—and not have a real reason to curse at your controller when you get scrubbed, but don't wanna (or can't) drop the money on the outrageously awesome Tournament Edition FightStick, this is a reasonable alternative, if you can actually find it for the $US40 MSRP.
P.S. If you wanna play Street Fighter IV with me, @reply me on Twitter and we'll set something up later this week.