I like Puppy Linux. It's the fastest OS, as it runs from RAM. I'm using Lucid 5.2.8 (based on Ubuntu) on a 10 year old laptop, and it runs great. I've also used Ubuntu 10.04 a couple years back on a Dell box, and I really liked it.
In the future, I would like to use Fatdog64 (a Puppy Linux distro, 64 bit) and Linux Lite.
My main computer is an HP box running Vista. It runs great.
I'm interested in Chrome OS, and may get a Chromebook one of these days.