I actually started writing something about this last night, but it got too long. I think that for the average (non-geeky) user, hardware support is the big issue, and I'm happy to say that things are getting better all the time. I've heard good things about Red Hat / Fedora, Mandriva and a few others, but I've been using Ubuntu versions for the last couple of years exclusively, so that's all I can really comment on. On my netbook (eee PC 1000) I had to tweak it to get it going the first time, but they now support it directly, and the "Netbook Remix" version comes with a "front end" adapted to the smaller screen.
Another question is the "look and feel" you want. If you really need it to be as much like Windows as possible, look for one that uses KDE as its graphical interface: Mandriva, Kubuntu. If you like something cleaner and a bit more UNIX-like, look for Gnome: Ubuntu, SuSE. I believe that Fedora installs both by default, and on the others you can always switch from one to the other after installing some extra bits.