All of these things ... and there are a great many of them ... are distros.

The folks who put together distros take on the job of assembling a sensible-to-them arrangement of literally hundreds of pieces of software (of which "the Linux kernel" is only one...) so that it all works together, and packaging them up in such a way that "it all just works," and so that you probably have no idea just how incredibly difficult a job it is.

They want the system to "just work" on whatever hardware you happen to own.

Red Hat, Inc. went almost immediately to the pure-commercial model. To get their system, and to get ongoing support for it, you buy it. This is how they pay their bills. Other "distro" efforts take a different approach, relying more on volunteers and contributions.

There is just downloading and installing CentOS or Scientific, as they're literally just RHEL without the Redhat branding and paid support, pretty much, and I ran Fedora for three months, it's a nice distro, however the one thing I dislike about it is it's a cutting-edge distro, but it's not a roller, and I'm generally a bigger fan of rollers if I want cutting-edge and/or bleeding-edge, which Arch brings to the table, and I've been running Arch in the form of Archbang for two months now, and love it, however I do wanna set up real Arch at some point.

Debian Stable and Ubuntu LTS would be a good enterprise distro as well, really stable repos, and easier to manage than RHEL, CentOS, or SLES and SLED, and Debian Stable has three years support while Ubuntu LTS has five, which, all in all, wouldn't be too bad a deal IMO.

Meanwhile on the homefront, Fedora, Debian Testing or Sid, OpenSUSE, Ubuntu standard or Ubuntu +1, or Arch would be better as you're not really running any critical stuff that requires as little downtime as possible at home like you would be in a professional setting.

In conclusion, if you're looking for a distro to run in enterprise, you'd be better off looking at Debian Stable, Ubuntu LTS, CentOS, RHEL, or SLES and SLED because of support and stability, while in the home, you'd be fine with Debian Testing or Sid, Ubuntu Standard or +1, Fedora, OpenSUSE, or Arch as you're not really concerned about stability on your home computer like you would be in an enterprise setting.

Just my $0.02.

Both SUSE and Red Hat charge you money (RH slightly more), because they offer support. Both are really aimed at large companies, and local tradition plays a part in the choice: USA leans to Red Hat (e.g. New York Stock Exchange) and Europe to SUSE (e.g. London Stock Exchange). Red Hat is best with Gnome, SUSE with KDE.

Companies who don't want to pay for help go for Debian or CentOS (99% the same as Red Hat), which are the main distros on web servers. On a desktop, CentOS is better (no flame wars, please) because it has lots of GUI configuration tools which Debian lacks.

SUSE is based on OpenSUSE and Red Hat on Fedora. Those offer more up-to-date software and are nice if you have some experience and fairly modern hardware, but they can't offer a high level of reliability.