Played a lot of hours of TMNF on keyboard before moving to an Xbox 360 controller. This massively improved my game-play experience, and led to an almost immediate purchase of TMUF, which I played exclusively with a controller.
Don't expect I'd ever move back to keyboard. In fact, I have a spare controller I can pull out in case of emergencies
I started with TM2 so I cant talk about the previous TM games. I have only used keyboard so far but im struggling with getting better time, especially on tracks with important slides and im starting to think that a pad with analog stick would be better. Think ill try to get my PS3 controller's analog sticks to work to test it out.
I tried the KB but at nearly 60 I find it too difficult and I get cramps. My game on TM1 definitely improved when I started using a Playstation controller (PS1/2) with a usb adapter and am slowly improving on TM2. Its robust and feels good and I can sit back in my chair instead of being hunched over my keyboard ..... and with 12 buttons I can allocate a button for horn, speech, opponents on/off etc etc without reaching for the keyboard. However, my advice is to keep the Respawn/Restart/Retire button on the keyboard for obvious reasons lol Hope this helps