Obviously Ubuntu.
But I should point out that a lot of people like MEPIS not me personally buy just a suggestion for your poll.

I like Gentoo for it's flexability even shitty DELL's can run it fast cos you can really optimize the kernal in an easy way.

I like Ubuntu/kubuntu cos you can chuck it on old laptops and pc's and it's easy peasy!

I like suse/ubuntu/fedora/mandriva but they hate my machines!

Got to love texstars PCLinux OS though

I forgot to mention why I like Ubuntu. I like debian distros for one and also I just like the community. As for MEPIS it is also a debian distro and the latest version is actually based off of Ubuntu the only difference is that it comes with porprietary (not opensource) software and I think to install it you have to pay for it, but the livecd (simplyMEPIS) is free.

I like ubuntu on the desktop because I like Gnome and I like having all my hardware discovered first time.

I run Redhat (well, CentOS) on my servers because I'm more familiar with it (used it since version 7.2).

Depending on what im using the linux distrobution for. I prefer Fedora, centOS and Debian.

Just for kicks, you should look at the poll that was posted on Cboard:
http://cboard.cprogramming.com/showthread.php?t=81459

SuSe 10.1 becuase I made some of the security scripts for it!

Ubuntu may be ok for just casual users, but is terrible for c/c++ programming. I tried it on my computer, easy to install but does not include any developers tools such as GNU compilers. I now use fedora 5 which is a lot more complete. Don't know anything about the other versions of linux.