Scientific Linux is a rebuild of Red Hat Enterprise Linux. It started out before the CentOS project really took off. Nowadays CentOS is officially supported by Red Hat, but Scientific Linux still exists on its own.
Since both CentOS and Scientific Linux are just rebuilds of RHEL, all three should be binary compatible, and you should be able to use the same software repositories for all three.
The Fedora project is where development of RHEL happens, and the Fedora project also ships software for RHEL releases that haven't been included in the official Red Hat package selection. There is a fair number of matter modeling packages in the Fedora Extra Packages for Enterprise Linux (EPEL) repositories.
However, the problem with RHEL is that since the distribution is "stable", with the current pace of development the system packages quickly become outdated. The widest and most up to date selection is within Fedora, which aims at a new stable release every 6 months.
IMNSHO there are only two distributions that can be considered at earnest for general usage: Debian/Ubuntu, and Fedora/Red Hat (and its clones like Scientific Linux and CentOS), since they are the most widely used and offer by far the widest software selections. (Knoppix is a live CD version of Debian.)
In my personal experience the Debian world tends to lag a bit behind, but it should be noted I am not impartial: I've been packaging for Fedora/Red Hat for over a decade, by addressing any deficiencies wherever I've noticed them; this is why my needs are best served by Fedora and Red Hat.
In any case, the situation dependends highly on the package and its maintainer. If the distribution has a contributor who needs package X for their interests, it's highly likely that the distribution's package X is up to date and includes all features. If not, then it might be that X is not included in the distro, or that the version of X is super old...