Using software is simple and anyone with reasonable intelligence who has ever seen the software in operation can use it.
installing, updating, administrating is another matter...
some can easily drive a stick shift and some can easily deal with a package problem....others fall to pieces regarding either one...
So is a beginner's linux one that is easiest to drive, or easiest to maintain or easiest to install? Or just easiest to drive?
If it's just easiest to drive- an expert could set up and maintain any linux for a user and it would then be easy to drive... So by that definition they would all be beginner's linux from gentoo to ubuntu.
On the other hand, if it is easiest to maintain and install and get up and working properly, the list becomes much shorter (I would think regular mint and pclos and variants, maybe ubuntu).
At any rate, just my opinion.
Like I said- I am really enjoying LMDE for myself.