I've used Ubuntu for a month, and *hated* it. I'm not going to rant about it here, it's boring and I have better stuff to do.
I installed ArchLinux last weekend, and that seems to work much better. I now have to deal with systemd, which sort of sucks, but I'll admit the boot/shutdown times are impressive (it's damn close to instantaneous, better than upstart, and much better than rc.d).
The installer (or rather, lack thereof) is also a bit of a pain; you have to manually fdisk/newfs everything. If you want "fancy" setups like lvm, encrypted filesystems, etc. you all have to do that manually
I like that you start with a simple base system, and add stuff yourself (unlike Ubuntu, where you start with a large complex system, and have to remove stuff). pacman also works pretty good (unlike apt-get, which should be renamed to apt-fail).
The documentation (ArchLinux wiki) is also pretty good, it's like the FreeBSD handbook, but better (probably because it's so much easier to contribute, who wants to muck about with docbook?).
I also looked at SlackWare, and it looks interesting, but was put off by the lack of an USB installer (I'm sure it exists, but wasn't able to find it within 5 mins), and the lack of packages for some common software I use (like my preferred WM).
My *first* choice was Fedora by the way, the reason being that I'm somewhat familiar with Fedora & CentOS, but wasn't able to install it due to quirks in the Fedora installer & my laptop...