[Karibou]

I've never exactly tried driving a robot with a PS2 controller, but the idea seems a little weird to me. Our team used two joysticks this year, one for the drivetrain and one for the arm, so I suppose that using a controller could combine the two. The right analog stick could be used for the arm, left for the robot, etc. So making the switch to a controller could save us a couple of pounds on the OI.
As said before, driver preference plays a pretty big part in it. Not being a driver, I was able to easily drive the robot during practices using joysticks with no prior joystick-type-controller experience. On the other hand, I've used (and umm...successfully destroyed) a PS2 controller before, but I don't think that I would feel comfortable using it to drive a robot. Then again, I play Final Fantasy, not Gran Turismo.
I'm not sure how the coding for a controller would work, but if your robot had a lot of functions, using all the buttons on a controller could be to your advantage (if it's possible to code it in--again, I don't know squat about programming this stuff). Using joysticks wouldn't be very practical.

Control-wise...it's been said that joysticks do allow fine movement, but then again, PS2 controllers can be very sensitive (assuming they're brand new and haven't been broken yet...). If you use a controller--assuming you use the analog sticks to drive the bot--you're only using one finger to control the bot. Just from playing Final Fantasy, I've found that yes, my thumb CAN slip off the stick when I'm pushing on it, or trying to turn quickly. In a video game, it probably won't matter much, but during a match, it could mean you lose the match. If your driver is skilled at using a controller, this might or might not happen. However, with a joystick, you're most likely using your entire hand to operate the controller, so you have a better grip on it and aren't likely to slip.

So I guess it really does depend on the bot's functions, and the driver preference/ability.
Of course, I could just be extremely biased towards joysticks, that being all I've ever used to drive a bot...

Somehow, I feel as if I've thought this out too much... o.O