I don't know if this has already been done (probably has), but I'm doing it anyways. I'll start. Arch Linux.
Ubuntu is probably my favorite. It's just so easy to navigate and use. Others I've used: Fedora Kubuntu Knoppix Debian Gentoo Redhat
Well i only have one flavour of linux running at the mo and that's Kubuntu on my netbook, seems good so far
Ubuntu has the best community and it is the most widely used which allows the OS to work out the bugs more quickly. It is also the easiest to use
My favorite is Arch, unless I'm managing a web server then Debian. If the question was expanded to Unix-like OS's I'd say OpenBSD though (for the web server comment, I didn't like using it as a desktop OS)
Scrap my previous post as i couldn't get WiFi to work... now installed Bodhi Linux and seems good so far Would recommend for a netbook/laptop
Backtrack 4................Its Great On My Laptops And On My Desk Tops. It Is Not Super Easy To Use Though So Not Good For Nix N00bies. :-}