See frankly it doesn't matter which one you go for unless certain hardware doesn't work on all the distros. You can go for ubuntu/suse/FC/mandriva/linspire/PCLinux OS,etc. All are good for newbies.
In 6.06 you will get updates till 1.5 yrs (7 months almost gone) whereas for 6.10 it will be till 7.04 releases. But, you can always upgrade to 7.04 after installing 6.10 or you can choose to live without updates(dangerous). That's the only support you get.
32 bit is recommended for newbies. 64 bit will still take some time to mature.
Kubuntu has KDE desktop whereas Ubuntu has GNOME desktop, Xubuntu has XFCE.
I read today, that for 7.04 there's gonna be one more version, Mubuntu (check ubuntu forums) or
http://ubuntustudio.org/
QwertyManiac has tried Ubuntu christmas edition and told me that he didn't like it so much. But, it's advantage is that it has a lot of proprietory softwares pre-installed which many distros do not have like mp3 support, flash, etc.