Ubuntu has <i>very</i> exhaustive support 'out-of-the-box' for hardware. Nearly all, if not all hardware you choose should be fine with it. You will need to note that the 64-bit install is different to the 32-bit install, and that you cannot use 64-bit on a 32-bit processor.

Gentoo is good. Ubuntu is better for newbies. Ubuntu's package manager, Synaptic, is extremely easy to use for newbies; you won't have to worry about dependencies with it. Gentoo's package manager, Portage, is also very nicely done, though much harder to read if you don't know what's going on.
Just a sidenote - Gentoo is notoriously hard to install for newbies. Having said that, the support provided is very good.

As bipper said earlier, Ubuntu (or Kubuntu, if you like KDE better) is very much based around the x window server, so you most likely won't be using a command line much. Gentoo is slightly less so, but not that much. One thing to notice is that Ubuntu uses Gnome; Kubuntu uses KDE.

If you want easy to use and learn on, I recommend Ubuntu.