I've been playing with an Xbox style controller too. The biggest gripe I have is with the D-pad and directional button-presses often registering as more than one (a diagonal) button-press. This literally makes PIP adjustment infuriating - especially when it matters; other maneuvers are affected too. I've been hoping to find a controller that uses four distinct buttons for the D-pad instead of the common rocker arrangement. That's not easy, especially in the asymmetric layout that I prefer greatly for ED (left joystick is above the D-pad). Yes, I have tried both layouts.
In lieu of that, I thought I'd try a high quality controller. Seeing as how that costs a bit more, if anyone has opinions/experience about/with controllers such as the Microsoft Elite Series II or the Scuf Prestige (SteelSeries, maybe), I'd like to hear them. My thought is, if it's not likely to be better, I'd rather consider the jump to a more serious rig because (especially as my skills grow) I get the distinct feeling that my success/ability is limited by the use of this type of controller.
Other than the issue with the D-pad, I've also noted some longevity issues. Specifically, ED has a large number of control to accommodate so pressing the joysticks to access those secondary functions is used all the time. This has lead to the joystick I use for Yaw to wear, lean, etc. in a couple of instances.
Happy travels, CMDRs!