For desktop systems:

I prefer trackballs. I have carpal, and I can tell you from experience that trackballs aggravate less. Thank you Logitech for the Trackman Marble. It is 'teh awesome'.

For Laptops:

I prefer the IBM Trackpoint system. It is extremely accurate.

Although being able to use 2 fingers to right click on my PB is cool.

Overall I prefer IBM Thinkpads. Quick and sexy, with dual inputs, removeable drive bay, excellent graphics (by my standards) and great keyboards.

My dream laptop:

A Thinkpad T61p built by Apple with full support for OS X and has a backlit keyboard and dual inputs. I can dream can't I?

I will never own another laptop without the backlit keyboard. I heart it that much.