Which tiling window manager is easiest to install and use inside of GNOME

Solution 1:

The only one I can think of that is specifically designed to work within the traditional Gnome setup is Bluetile.

Solution 2:

There's a fairly comprehensive review of available tiling window managers in this AskUbuntu post; any one supporting EWMH will work with GNOME.

Regarding XMonad specifically, I have it running by placing this single line in my ~/.gnomerc (will work for any window manager, not just xmonad):

export WINDOW_MANAGER=xmonad

No need to create a different session type: just choose the standard GNOME one. When you want to revert back to metacity/compiz, remove the WINDOW_MANAGER line from ~/.gnomerc.