I use Ubuntu, because I wanted to switch from windows to linux anyway and ubuntu has a very nice packaging mechanism (but I don't know other Distros, it might not be the best).
You can also find very much information in the internet about ubuntu. A friend has Ubuntu, so this biased my decision, too.
If I want to try out KDE then I can install it in ubuntu, too, so this was not part of the decision for me.
I suppose that the rockboxdev.sh script and a good editor will run on every (major) distro in the same way, so it only matters if you want to use Linux for more than just programming.