I’m running all three at home now. I’m most satisfied with Ubuntu (Jaunty Jackalope).
It’s free, fast (running on a seven-year-old machine like a champ), and provides a pretty big sense of accomplishment. Even enjoying the command line.
The Mac is still the fave (I like the juicy iMac screen), but it comes with random shutdowns. Plus, I hate the Mighty Mouse.
But for the price, Ubuntu is king.