My personal favorite was Fedora 14, it was perfect! But all good things have an end. Then came Sabayon, which I ran for months until it became, meh. My other used to be Chakra OS, but KDE 5 pooped all over that distro for me.
Now it's a real toss up between Linux Mint, Ubuntu, Manjaro, Mageia, elementary, and Bodhi. I know a lot are based on Ubuntu, but I love Ubuntu-based distros, mostly because they take in such interesting directions.
My least favorites in case anyone was wondering would have to be Windows and Debian Stable. Windows because I just don't care for it and I don't like using it and Debian Stable because fuck that update cycle. Maybe for a server, Debian stable is nice, but for desktop, there's no excuse to hold onto old software for "stability."