Easy Debian is actually just a set of scripts, developed by qole, which allow you to mount a debian partition or image and launch applications along side maemo. Whether you use qole's images, or Deblet, it matters not.. Easy Debian is just the scripts (as was said by qole himself).

Now the more appropriate question would be the difference in Qole's Debian Image or the Deblet ... Qole's image is a stripped down version of debian made solely for the purposes of the chroot.. while Deblet is a full OS meant to be booted - which means it's slightly larger - but can still be run via the Easy Debian scripts with minimal difficulty. Deblet Installer is moving to include an "Easy Debian" method to where it will download an image, or build a deblet, and setup Easy Debian for you.. when this evolution is complete there will be no difference - Script or Debian wise - between the two.,

I have done no official testing but I can tell you that I get considerably less battery life when using Debian booted. Using Easy Debian isn't that much more of a battery drain than Maemo. No more than launching any other application.

As far as stability.. I have had no problems with my Deblet install and it's all I use now that there is sound and Flash. The video is still being worked on. Camera works.
There is not one for deblet; You have to choose when you install what you want. With Qole's Debian Image it comes with IceWM.. which can be changed to use KDE / Gnome / XFCE / whatever with some script modification. As Benson pointed out.. XFCE, Gnome, and KDE are "heavyweight" desktops.. they will slow everything down beyond what true "Lightweight" desktops will; IE: IceWM, Window Maker, FluxBox, OpenBox, and LXDE.
Use the Deblet Installer For Maemo.. completely graphical utility that walks you through setting up deblet on your Internal or External memory. Once deblet is built/installed.. you can decide if you want Easy Debian, or just to boot to it.. or both. There are plenty of explanations on using Easy Debian with Deblet around.. but essentially all you need to do is install the Easy Debian package from Qole and edit the /home/user/.chroot file.. It's commented very well.