Let me see...
For ease of use, especially for former Mac users, I recommend
Ubuntu, which does run on slow/low end machines well.
SUSE is very good, especially for slow machines, but obviously you'll want
openSUSE, the free open source version.
However, if your machine is not
old, just
low end, you want a distro that is
extremely easy to use, all heads should turn to
Freespire.