I selected Mepis primarily because of the MEPIS User Guide http://www.mepis.org/node/6679
The Mepis documentation is generally better than other distributions, especially better for newbies with Windows experience. That User Guide is a good example of that better documentation.
I suggest reading some of the Mepis documentation. Quite a lot of it will be helpful even if you select another distribution, such as Ubuntu. If you share my opinion that it is better documented, you'll probably also like the others ways it is slightly different (I think better) than the other distributions I tried.
The liveCD for Mepis was also more robust across the selection of computers I tested than other combination liveCD/Install distributions. But since you seem to be OK already with the Ubuntu liveCD, that shouldn't be a factor for you.