I started with RedHat back in the day, but if you really want to understand how the Linux kernel works and what goes into creating a Linux operating environment (i.e. a "distro"), then your best option is probably Gentoo. If you just want to see what a bloated KDE or Gnome installation looks like with all the bells and whistles enabled, then any distribution that offers a "LiveCD" with a GUI will suffice.
Trev
