Your question of "one vs other" is from a point that you probably dont want to get involved with Linux anymore than necessary to create a disk and install/enjoy.
Asking me for a blow by blow is probably going to cause war, but its your thread, so you know, I'm not subscribed to this because I dont want conflicts.
Xbmcbuntu is too heavyweight and old, installs things like lightdm (tons of dependencies) which are totally unneeded and xwindow managers (argh). however you can do whatever you want with your machine.
Openelec is simply a HTPC install and go - not flexible enough to do what "I" want to do. and its not designed that way.
I want to compile xbmc from source, tinker with box, customize things to suit my changing needs, dont want to be locked into release cycles and I dont want to break xbmc because I upgraded my kernel or some other xbmcbuntu packages)
There's 3 choices irrespective: (more if you choose another arch)
Xbmcbuntu (if you want to have some control but dont care about random packages that are unneeded or are prepared to reinstall if you break it trying to upgrade it and are ok to wait for releases)
Openelec (if you just want it to work , its fast to install and dont care for the ease of tinkering and are ok to wait for releases)
xbmc minimal If you want newer Linux, less packages and have all flexibility. of Ubuntu specially the userbase to draw help from dont want to wait for anything,
Because xbmcbuntu installs uneeded packages and breaks way to easy -1
Because Openelec is not flexible enough for "my" needs/expectations -1
Ultimately you should try everything, like I did and come to your own conclusions and perhaps learn something about Linux in the process.
uNi
