64 bit Ubuntu here. I fooled around with Redhat a few times long ago, and never did make it run right, due to hardware issues and a total lack of support in my area. Around the time WinXP 64 bit came out, I bought an Opteron, and had problems with drivers. Went looking at Linux again, downloaded Suse 9.something, and it just worked. Right out of the box, it just worked!! Well, as time went by, I got more and more tired of administering Windows machines that seemed to be eaten up with malware every month or two, so I started a crusade to convert the family to Linux. The wife especially resisted, until I installed Ubuntu. Today, she uses a machine that dual boots to WinXP or Ubuntu - and she never boots to Windows.
On my machine, the gateway to the internet, I'm kinda stuck with Ubuntu now. It's been installed for so long, I hate to do a fresh install of anything, then try to migrate everything. If/when I get a new machine, I plan to go Debian.