Both Debian and Ubuntu Server offer various additions to improve the use-ability of many upstream Linux packages (e.g. especially Apache2). These include wrapper scripts, arguably better default settings, additional environment variables and out-of-the-box (available or pre-installed) tools, and more (e.g. Ubuntu's update-motd.d pam extension for builtin functionality of dynamic MOTDs using scripts). All are maintained to a very high standard by the developers (which can be said for all big linux distributions, of course).

The amount of packages available through apt far outweighs RHEL's yum. packages.debian.org offers a very nice and clear way to browse apt packages, with very well presented information about everything related to each (which releases have this package? short description; dependencies/recommends/suggests; downloads; all other relevant outlinks (changelog, developer info, bug tracker, ...)).

Upgrading Debian from one stable version to another is usually very easy and not painful, which is necessary considering it's relative fast releases.

Thus, my recommendation is to start out with Debian/Ubuntu Server and when you are confident enough with Linux and have moved from hand/tutorials-crafted (eventually messy) servers to precisely-defined provisioned-servers move to a RHEL distribution because you don't need the benefits of Debian anymore and should prefer RedHat's stability and confinedness to less releases and more-upstream-like Linux.