I use a combination of 360 pads, Sixaxis/Dualshocks, and Wiimotes... 360s for the nice feel and thumbsticks, DS'es for the D-pads, and Wiimotes for Dolphin and the occasional NES/SMS emu.
Since I already have them by virtue of owning the consoles (don't actually have a 360 lol) it just seems more economical to have them pull double duty instead of having yet another set of controllers just for the PC.
The Logitech game pads are okay, nothing special. It's true the LT/RT are pretty stiff, they feel like they have an unnecessarily strong return spring. Great for throttle control in driving games, not so good for shooters. The major complaint I've heard about the analogs is a square shaped movement area, but the new ones fixed that issue.
The 360 controller is definitely superior, but imo not worth dropping $60 on a new controller. Personally I'm more used to the dualshock layout anyway.